Fix issue causing our spec suite to run much slower.

Created by: myronmarston

Before this change:

$ bin/rspec | egrep 'Finished|(examples.*failure)'
Finished in 45.99 seconds (files took 0.89765 seconds to load)
2014 examples, 4 failures, 1 pending

After this change:

$ bin/rspec | egrep 'Finished|(examples.*failure)'
Finished in 11.16 seconds (files took 1.16 seconds to load)
2014 examples, 4 failures, 1 pending

I believe the issue was requiring 'rspec/rails/version'. Since rspec-rails is not available, rubygems would exhaustively search all my installed gems before raising LoadError. I have ~300 gems installed and this was quite slow.

It's better to just force it to raise LoadError and not wait on RubyGems to do the same thing.