Add ability to match errors on case equality

[ianks]

The semantics of rspec-retry's rescuing are a bit different than ruby's rescue. Ruby will rescue classes based on the case equality operator as well (===). This blog post describes is very well

With this PR, users will be able to dynamically retry on errors.

Let me know if you have any thoughts 😄

[michaelglass]

Will merge this when tests pass. Also: thanks for the explanation. Neat! Another way for ruby to do something surprising 👅

[ianks]

@michaelglass it looks like ruby gems went down for one of the specs. can you retrigger?

[michaelglass]

restarting travis over and over again is a good way to ensure your tests are reliable, right? Thanks for the change.