Restore strong parameters matcher

This restores the strong parameters matchers which were removed in [f107ba0](https://github.com/thoughtbot/shoulda-matchers/commit/f107ba014c8ab85bde70ce33e8176b21739bf714) due to issues with bourne integration. I've removed the bourne require from the matcher and it appears that now with the integration of bourne into RSpec everything works cleanly once again.