Fix clickable links for RSpec 3 (again)

This was first fixed in https://github.com/rspec/rspec-tmbundle/pull/69 for early beta versions of RSpec 3, but since then there have been changes in RSpec so that the original fix no longer works.

Fortunately, this fix is even simpler than the original version. Tested with RSpec 3.0.0.beta2, RSpec 3.0.0 and RSpec 3.0.3 (older versions are not affected from this change as they do not use `RSpec::Mate::Formatters:TextMate`).