Twitter bootstrap – Heroku Application Error (Ruby 2.2.2)

I have a Rails app and I try to push it to Heroku. After I pushed it to Heroku, I get Application Error message.

When I run heroku logs -n 300, I get this (sorry for pasting the logs in Gist. StackOverflow not allowing me to post >30K characters question).

This is my Gemfile:

source 'https://rubygems.org'


# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '4.2.1'

# Use SCSS for stylesheets
gem 'sass-rails', '~> 5.0'

# 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'

# Use jquery as the JavaScript library
gem 'jquery-rails'

# Twitter Bootstrap
gem 'bootstrap-sass', '3.2.0.0'

# 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

# Devise for user auth
gem 'devise'

# CanCanCan for user roles
gem 'cancancan', '~> 1.10'

# Gravatar
gem 'gravatar_image_tag'

# Font Awesome
gem 'font-awesome-sass'

group :development, :test do
  # Use sqlite3 as the database for Active Record
  gem 'sqlite3'

  # Call 'byebug' anywhere in the code to stop execution and get a debugger console
  gem 'byebug'

  # Access an IRB console on exception pages or by using <%= console %> in views
  gem 'web-console', '~> 2.0'

  # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
  gem 'spring'
end

group :production do
  gem 'pg',             '0.17.1'
  gem 'rails_12factor', '0.0.2'
end

ruby "2.2.2"

I thought that the error is because I’m not running rake db:migrate on Heroku. But, after I run heroku run rake db:migrate, the error is still same.

What should I do?

Note: This app runs well on my localhost.