Sort of fix undefined method or local variable "assets_environment "

I stumbled upon the same error as referenced in this issue https://github.com/pivotal/jasmine-gem/issues/184 within a rails 4.0.2 application.
It seems that the integration with https://github.com/rails/sprockets-rails/ is somehow broken.
Looks like this block https://github.com/rails/sprockets-rails/blob/master/lib/sprockets/railtie.rb#L64-L125 never runs and therefore ```assets_environment``` never get set.

This is of course by no mean a proper fix, just a quick insight of my investigations.