Gemfile

group :development, :test do
  # ...

  if RUBY_PLATFORM.downcase.include?("darwin")
    gem 'rb-fsevent'
    gem 'growl'
  end

  if RUBY_PLATFORM.downcase.include?("linux")
    gem 'libnotify'
    gem 'rb-inotify', '~> 0.8.8'
  end
end

log

 ** [out :: staging] You are trying to install in deployment mode after changing
 ** [out :: staging] your Gemfile. Run `bundle install` elsewhere and add the
 ** [out :: staging] updated Gemfile.lock to version control.
 ** [out :: staging] 
 ** [out :: staging] You have added to the Gemfile:
 ** [out :: staging] * libnotify
 ** [out :: staging] * rb-inotify (~> 0.8.8)
 ** [out :: staging] 
 ** [out :: staging] You have deleted from the Gemfile:
 ** [out :: staging] * growl
 ** [out :: staging] * rb-fsevent