Fixes ability of requiring font-awesome assets

[grzuy]

Steps to reproduce the issue:

• Create a brand new rails 4.2.4 app
• Create a rails route + controller + view that uses application layout
• Add gem 'wysiwyg-rails' to the Gemfile
• Following usage instructions (https://github.com/froala/wysiwyg-rails#usage):
  • Add require to the application.js
  • Add requires to the application.css
• Visit new route
• Exception thrown couldn't find file 'font-awesome' with type 'text/css'

The problem being that the font-awesome-rails assets are not included in asset search path (i.e Rails.application.config.assets.paths). The requirement of the dependency should fix this.

More details: https://github.com/bokmann/font-awesome-rails#rails-engines https://bibwild.wordpress.com/2013/02/27/gem-depends-on-rails-engine-gem-gotcha-need-explicit-require/

[grzuy]

Related: https://github.com/bokmann/font-awesome-rails/issues/130