Sustainable testing

In RSpec3 if you're using `rspec-rails` gem it generates two helpers:
* `rails_helper.rb` – basically what `spec_helper` used to look like and 
* `spec_helper.rb` – same behaviour as running `rspec --init` (not Rails specific)

Shall we stick to the same behaviour i.e. If the `.rb` is not a Rails specific class (controller / model) you should always require just the new `spec_helper`?

More info about the change: https://www.relishapp.com/rspec/rspec-rails/docs/upgrade