Update tests to support RSpec 3.0.0.beta1

This bumps the RSpec version to 2.14.1 and updates the tests to use the `expect` syntax.  RSpec 3.0 removes the `should` syntax, so this prepares the gem for supporting RSpec 3.0.

The test suite is green using RSpec 2.14.1 and RSpec 3.0.0.beta1.

More information about RSpec 3.0:  http://myronmars.to/n/dev-blog/2013/11/rspec-2-99-and-3-0-betas-have-been-released