I have the following rails configuration:
Windows 7 Rails 4.1.1 Ruby 2.0.0p481 Gem: coffee-rails 4.0.1 Gem: coffee-script 2.3.0 Gem: coffee-script-source 1.9
I think renaming extension is not good solution. Try following:
Add to Gemfile
gem 'coffee-script-source', '1.8.0'
then, run
bundle update coffee-script-source
and restart the server (if needed)