Twitter bootstrap – Sass::SyntaxError: Undefined variable: "$fa-css-prefix"

I am trying to integrate the present theme in my rails app. After intgerating when I run

rake assets:precompile --trace

I get the following error.

** Invoke assets:precompile (first_time)
** Invoke assets:environment (first_time)
** Execute assets:environment
** Invoke environment (first_time)
** Execute environment
** Execute assets:precompile
rake aborted!
Sass::SyntaxError: Undefined variable: "$fa-css-prefix".
/home/munam/projects/infotachus/ror/nutritious_dec_28/app/assets/stylesheets/_animated.scss:4
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/script/tree/variable.rb:49:in `_perform'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/script/tree/node.rb:50:in `perform'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/script/tree/interpolation.rb:170:in `_perform'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/script/tree/node.rb:50:in `perform'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/visitors/perform.rb:540:in `block in run_interp_no_strip'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/visitors/perform.rb:538:in `map'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/visitors/perform.rb:538:in `run_interp_no_strip'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/visitors/perform.rb:545:in `run_interp'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/visitors/perform.rb:410:in `visit_rule'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/visitors/base.rb:36:in `visit'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/visitors/perform.rb:158:in `block in visit'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/stack.rb:79:in `block in with_base'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/stack.rb:115:in `with_frame'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/stack.rb:79:in `with_base'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/visitors/perform.rb:158:in `visit'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/visitors/base.rb:52:in `block in visit_children'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/visitors/base.rb:52:in `map'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/visitors/base.rb:52:in `visit_children'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/visitors/perform.rb:167:in `block in visit_children'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/visitors/perform.rb:179:in `with_environment'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/visitors/perform.rb:166:in `visit_children'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/visitors/base.rb:36:in `block in visit'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/visitors/perform.rb:186:in `visit_root'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/visitors/base.rb:36:in `visit'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/visitors/perform.rb:157:in `visit'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/visitors/perform.rb:8:in `visit'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/root_node.rb:36:in `css_tree'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/tree/root_node.rb:20:in `render'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sass-3.4.20/lib/sass/engine.rb:278:in `render'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/sass_processor.rb:74:in `block in call'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/utils.rb:154:in `module_include'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/sass_processor.rb:73:in `call'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/sass_processor.rb:30:in `call'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/processor_utils.rb:75:in `call_processor'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/processor_utils.rb:57:in `block in call_processors'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/processor_utils.rb:56:in `reverse_each'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/processor_utils.rb:56:in `call_processors'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/loader.rb:134:in `load_from_unloaded'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/loader.rb:60:in `block in load'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/loader.rb:318:in `fetch_asset_from_dependency_cache'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/loader.rb:44:in `load'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/cached_environment.rb:20:in `block in initialize'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/cached_environment.rb:47:in `yield'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/cached_environment.rb:47:in `load'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/bundle.rb:23:in `block in call'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/utils.rb:183:in `dfs'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/bundle.rb:24:in `call'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/processor_utils.rb:75:in `call_processor'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/processor_utils.rb:57:in `block in call_processors'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/processor_utils.rb:56:in `reverse_each'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/processor_utils.rb:56:in `call_processors'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/loader.rb:134:in `load_from_unloaded'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/loader.rb:60:in `block in load'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/loader.rb:318:in `fetch_asset_from_dependency_cache'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/loader.rb:44:in `load'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/cached_environment.rb:20:in `block in initialize'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/cached_environment.rb:47:in `yield'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/cached_environment.rb:47:in `load'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/base.rb:66:in `find_asset'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/base.rb:73:in `find_all_linked_assets'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/manifest.rb:142:in `block in find'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/legacy.rb:114:in `block (2 levels) in logical_paths'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/path_utils.rb:225:in `block in stat_tree'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/path_utils.rb:209:in `block in stat_directory'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/path_utils.rb:206:in `each'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/path_utils.rb:206:in `stat_directory'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/path_utils.rb:224:in `stat_tree'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/legacy.rb:105:in `each'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/legacy.rb:105:in `block in logical_paths'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/legacy.rb:104:in `each'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/legacy.rb:104:in `logical_paths'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/manifest.rb:140:in `find'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/sprockets/manifest.rb:168:in `compile'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-rails-3.0.0/lib/sprockets/rails/task.rb:68:in `block (3 levels) in define'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-3.5.2/lib/rake/sprocketstask.rb:147:in `with_logger'
/home/munam/.rvm/gems/ruby-2.2.3@Nutritious/gems/sprockets-rails-3.0.0/lib/sprockets/rails/task.rb:67:in `block (2 levels) in define'
/home/munam/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/rake/task.rb:240:in `call'
/home/munam/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/rake/task.rb:240:in `block in execute'
/home/munam/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/rake/task.rb:235:in `each'
/home/munam/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/rake/task.rb:235:in `execute'
/home/munam/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/rake/task.rb:179:in `block in invoke_with_call_chain'
/home/munam/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/monitor.rb:211:in `mon_synchronize'
/home/munam/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/rake/task.rb:172:in `invoke_with_call_chain'
/home/munam/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/rake/task.rb:165:in `invoke'
/home/munam/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/rake/application.rb:150:in `invoke_task'
/home/munam/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/rake/application.rb:106:in `block (2 levels) in top_level'
/home/munam/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/rake/application.rb:106:in `each'
/home/munam/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/rake/application.rb:106:in `block in top_level'
/home/munam/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/rake/application.rb:115:in `run_with_threads'
/home/munam/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/rake/application.rb:100:in `top_level'
/home/munam/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/rake/application.rb:78:in `block in run'
/home/munam/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/rake/application.rb:176:in `standard_exception_handling'
/home/munam/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/rake/application.rb:75:in `run'
/home/munam/.rvm/rubies/ruby-2.2.3/bin/rake:33:in `<main>'

I have three folders in my theme

1. less
2. css
3. scss

When integrating into my app I have merged files of these folders in one folder.

app/assets/stylesheets

Here are the gems in my gemfile.

source 'https://rubygems.org'


# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '4.2.5'
# Use sqlite3 as the database for Active Record
gem 'pg'
# Use SCSS for stylesheets
# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '>= 1.3.0'
# Use CoffeeScript for .coffee assets and views
gem 'coffee-rails', '~> 4.1.0'
# See https://github.com/rails/execjs#readme for more supported runtimes
# gem 'therubyracer', platforms: :ruby

# Use jquery as the JavaScript library
gem 'jquery-rails'
# Turbolinks makes following links in your web application faster. Read more: https://github.com/rails/turbolinks
gem 'turbolinks'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 2.0'
# bundle exec rake doc:rails generates the API under doc/api.
gem 'sdoc', '~> 0.4.0', group: :doc

# Use ActiveModel has_secure_password
# gem 'bcrypt', '~> 3.1.7'

# Use Unicorn as the app server
# gem 'unicorn'

# Use Capistrano for deployment
# gem 'capistrano-rails', group: :development
group :assets do
  gem 'sass-rails', '~> 5.0'
  gem 'font-awesome-rails'
  gem 'font-awesome-sass'
  gem 'font-awesome-sass-rails'
  gem 'twitter-bootstrap-rails', :git => 'git://github.com/seyhunak/twitter-bootstrap-rails.git'

end

group :development, :test do
  # Call 'byebug' anywhere in the code to stop execution and get a debugger console
  gem 'byebug'
  gem 'dotenv-rails'
end

group :development do
  # Access an IRB console on exception pages or by using <%= console %> in views
  gem 'web-console', '~> 2.0'
  gem 'better_errors'
  gem 'binding_of_caller'
  # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
  gem 'spring'
end

gem 'devise'
gem 'amazon-ecs'
gem 'sucker'
gem 'vacuum'
gem 'actionpack-xml_parser'

I have only these two lines in my application.css

 *
 *= require_tree .
 *= require_self
 */

and this line in my config/initializers/assets.rb

Rails.application.config.assets.precompile += [/.*.png/,/.*.ico/,/.*.jpg/,/.*.js/,/.*.scss/]

I have tried all the threads on stackoverflow and github but nothing seems to work in my case. What to look for is still not clear. Any help would be really great. Lots of thanks in advance!