Support ActiveSupport >= 3.2, RSpec 3.x

@btakita, I don't know if you're still maintaining this, but I'm looking to use NamedRoutes for a webmachine-ruby project.

I've updated this to work with ActiveSupport 3.2 and higher (currently is running fine with up to the latest 4.1.6). No tests have changed except for switching `should` to `expect.to` syntax.