Fixes an issue which doesn't update assets cache with rails 4

What was happening:
1. Rails.application.assets.register_preprocessor was always raising
TypeError: can't modify immutable index.
2. The error was rescued so looks it's done. But context.depend_on is not
registered so locale files changes didn't expires cache.

I did some research and found
https://github.com/rails/rails/issues/2211#issuecomment-1724180
and simply removed ActiveSupport.on_load and everything is working well.