NoMethodError: undefined method `on' for main:Object – Twitter bootstrap

when I try to bundle exec cap production deploy --trace I get an error message:

deploy@h2540559:/www/apps/foodsoft$ bundle exec cap production deploy --trace
** Invoke production (first_time)
** Execute production
** Invoke load:defaults (first_time)
** Execute load:defaults
** Invoke rvm:hook (first_time)
** Execute rvm:hook
cap aborted!
NoMethodError: undefined method `on' for main:Object
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/capistrano-rvm-0.1.2/lib/capistrano/tasks/rvm.rake:17:in `block (2 levels) in <top (required)>'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/task.rb:248:in `call'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/task.rb:248:in `block in execute'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/task.rb:243:in `each'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/task.rb:243:in `execute'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/task.rb:187:in `block in invoke_with_call_chain'
/usr/local/rvm/rubies/ruby-2.0.0-p643/lib/ruby/2.0.0/monitor.rb:211:in `mon_synchronize'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/task.rb:180:in `invoke_with_call_chain'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/task.rb:173:in `invoke'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/capistrano-3.2.1/lib/capistrano/dsl/task_enhancements.rb:12:in `block in after'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/task.rb:248:in `call'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/task.rb:248:in `block in execute'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/task.rb:243:in `each'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/task.rb:243:in `execute'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/task.rb:187:in `block in invoke_with_call_chain'
/usr/local/rvm/rubies/ruby-2.0.0-p643/lib/ruby/2.0.0/monitor.rb:211:in `mon_synchronize'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/task.rb:180:in `invoke_with_call_chain'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/task.rb:173:in `invoke'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/application.rb:150:in `invoke_task'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/application.rb:106:in `block (2 levels) in top_level'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/application.rb:106:in `each'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/application.rb:106:in `block in top_level'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/application.rb:115:in `run_with_threads'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/application.rb:100:in `top_level'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/application.rb:78:in `block in run'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/application.rb:176:in `standard_exception_handling'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/rake-11.1.1/lib/rake/application.rb:75:in `run'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/capistrano-3.2.1/lib/capistrano/application.rb:15:in `run'
/usr/local/rvm/gems/ruby-2.0.0-p643/gems/capistrano-3.2.1/bin/cap:3:in `<top (required)>'
/usr/local/rvm/gems/ruby-2.0.0-p643/bin/cap:23:in `load'
/usr/local/rvm/gems/ruby-2.0.0-p643/bin/cap:23:in `<main>'
/usr/local/rvm/gems/ruby-2.0.0-p643/bin/ruby_executable_hooks:15:in `eval'
/usr/local/rvm/gems/ruby-2.0.0-p643/bin/ruby_executable_hooks:15:in `<main>'
Tasks: TOP => rvm:hook

Here is my gemfile:

# A sample Gemfile
source "https://rubygems.org"

gem "rails", '~> 4.2'
gem 'sass-rails'
gem 'coffee-rails'
gem 'less-rails'
gem 'uglifier', '>= 1.0.3'
# See https://github.com/sstephenson/execjs#readme for more supported runtimes
gem 'therubyracer', platforms: :ruby


gem 'jquery-rails'
gem 'select2-rails'
gem 'rails_tokeninput'
gem 'bootstrap-datepicker-rails'
gem 'date_time_attribute'
gem 'rails-assets-listjs', '0.2.0.beta.4' # remember to maintain list.*.js plugins and template engines on update
gem 'i18n-js', '~> 3.0.0.rc8'
gem 'rails-i18n'

gem 'mysql2'
gem 'prawn'
gem 'prawn-table'
gem 'haml-rails'
gem 'kaminari'
gem 'simple_form'
gem 'inherited_resources'
gem 'localize_input', git: "git://github.com/bennibu/localize_input.git"
gem 'daemons'
gem 'twitter-bootstrap-rails', '~> 2.2.8'
gem 'simple-navigation', '~> 3.14.0' # 3.x for simple_navigation_bootstrap
gem 'simple-navigation-bootstrap'
gem 'ransack'
gem 'acts_as_tree'
gem 'rails-settings-cached'
gem 'resque'
gem 'whenever', require: false # For defining cronjobs, see config/schedule.rb
gem 'protected_attributes'
gem 'ruby-units'
gem 'attribute_normalizer'
gem 'ice_cube', github: 'wvengen/ice_cube', branch: 'issues/50-from_ical-rebased' # fork until merged
gem 'recurring_select'
gem 'roo', '~> 1.13.2'
gem 'spreadsheet'

# we use the git version of acts_as_versioned, and need to include it in this Gemfile
gem 'acts_as_versioned', github: 'technoweenie/acts_as_versioned'
gem 'foodsoft_wiki', path: 'plugins/wiki'
gem 'foodsoft_messages', path: 'plugins/messages'

# plugins not enabled by default
#gem 'foodsoft_uservoice', path: 'plugins/uservoice'


group :production do
  gem 'exception_notification'
end

group :development do
  gem 'sqlite3'
  gem 'mailcatcher'
  gem 'web-console', '~> 2.0'

  # allow to use `debugger` https://github.com/conradirwin/pry-rescue
  gem 'pry-rescue'
  gem 'pry-stack_explorer'

  # Better error output
  gem 'better_errors'
  gem 'binding_of_caller'
  # gem "rails-i18n-debug"
  # chrome debugging extension https://github.com/dejan/rails_panel
  gem 'meta_request'

  # Get infos when not using proper eager loading
  gem 'bullet'

  # Hide assets requests in log
  gem 'quiet_assets'

  # Deploy with Capistrano
  gem 'capistrano', '~> 3.2.0', require: false
  gem 'capistrano-rvm', require: false
  gem 'capistrano-bundler', '>= 1.1.0', require: false
  gem 'capistrano-rails', require: false
  # Avoid having content-length warnings
  gem 'thin'
end

group :development, :test do
  gem 'ruby-prof', require: false
end

group :test do
  gem 'rspec-rails'
  gem 'factory_girl_rails'
  gem 'faker'
  gem 'capybara'
  # webkit and poltergeist don't seem to work yet
  gem 'selenium-webdriver'
  gem 'database_cleaner'
  gem 'connection_pool'
  # need to include rspec components before i18n-spec or rake fails in test environment
  gem 'rspec-core', '~> 3.2'
  gem 'rspec-rerun'
  gem 'rspec-legacy_formatters'
  gem 'i18n-spec'
  # code coverage
  gem 'simplecov', require: false
  gem 'coveralls', require: false
end

my capfile

# Load DSL and Setup Up Stages
require 'capistrano/setup'

# Includes default deployment tasks
require 'capistrano/deploy'

# Includes tasks from other gems included in your Gemfile
#
# For documentation on these, see for example:
#
#   https://github.com/capistrano/rvm
#   https://github.com/capistrano/rbenv
#   https://github.com/capistrano/chruby
#   https://github.com/capistrano/bundler
#   https://github.com/capistrano/rails
#
 require 'capistrano/rvm'
# require 'capistrano/rbenv'
# require 'capistrano/chruby'
# require 'capistrano/bundler'
require 'capistrano/rails/assets'
require 'capistrano/rails/migrations'

# Loads custom tasks from `lib/capistrano/tasks' if you have any defined.
Dir.glob('lib/capistrano/tasks/*.{cap,rake}').each { |r| import r }

and also my deploy.rb

#
# Capistrano 3 deployment configuration
#
#   http://www.capistranorb.com/
#   https://semaphoreapp.com/blog/2013/11/26/capistrano-3-upgrade-guide.html

# defaults that can be updated from the environment
set :branch,              ENV["REVISION"] || ENV["BRANCH_NAME"] || "master"

# you probably want to change these
set :application,         'foodsoft'            # application name (whatever you like)
set :domain,              'biomio-giessen.de' # host
set :user,                'deploy'              # ssh deploy user
set :keep_releases,       10
set :repo_url,            'git://github.com/foodcoops/foodsoft.git'
set :deploy_to,            "/www/apps/#{fetch :application}-#{fetch :stage}"

# more settings which are probably ok
set :log_level,           :info
set :linked_files,        %w{config/database.yml config/app_config.yml config/initializers/secret_token.rb config/initializers/session_store.rb}
set :linked_dirs,         %w{bin log tmp/pids tmp/cache tmp/sockets vendor/bundle public/system}

# assuming one server for everything, with one user for deploy and one for resque
server fetch(:domain), user: fetch(:user), roles: [:web, :app, :resque, :db]

# if you use RVM, uncomment the line in Capfile, and optionally uncomment rvm settings
# set :rvm_ruby_string,     :local

# task hooks
namespace :deploy do

  desc 'Restart application'
  task :restart do
    on roles(:app), in: :sequence, wait: 5 do
      # tell mod_passenger to reload the application
      execute :touch, release_path.join('tmp/restart.txt')
    end
  end

  after :restart, 'resque:restart'

  after :finishing, 'deploy:cleanup'

  # see lib/capistrano/tasks/plugins.cap
  #before 'bundler:install', 'enable_plugins:auto'

end

Does anyone know how to fix this?

Thank you very much,
Maxi