Fix Sprockets not working with Ruby 2

The issue was that with old strict dependency on Rails 3.2, when using Ruby 2, Sprockets would not correctly consider the include directives in css and js files. Original issue: https://github.com/sstephenson/sprockets/issues/352

Updated Rails version dependency in Gemfile so that the projects could
get version of Sprockets that would work correctly in Ruby 2.

Tested all 3 projects, after updating the assets are being processed correctly.