Add `rspec` gem to Cucumber definitions

* Fixes #259 issue via changes made in #262 
* Fixes #262 PR since its Travis build failed

It turns out that we needed to revert back to using `require 'rspec'` in `lib/shoulda/matchers/integrations/rspec.rb`, but also add in the `rspec` gem for when we build an app via Cucumber to mimic the added dependency done in #256.