Load rails environment when precompiling assets

* Setting config.assets.initialize_on_precompile to false does not load does not
  load Rails environment when precompiling assets
* Use of named routes in js.erb files requires Rails environment
* Heroku suggests setting to false in Rails 3, but this config option is not
  available in Rails 4 so seems most efficient to just remove
* source: https://devcenter.heroku.com/articles/rails-asset-pipeline

https://trello.com/c/0pwMUlS8