Upgrade to latest RSpec

Hi I noticed that you had some issues with the latest RSpec, this PR fixes the only spec that was broken for me on the latest version of rspec, so removes the explicit dependency and also removes some deprecation warning(s).

From what I can see the spec would pass coincidentally on RSpec 2.13, as the return value of the stubbed method would have been `nil`, not `false` as intended.

Of course if you had another issue I'd be happy to help investigate what it is :)