Not consider some Exceptions as failure

Hi,

I'm trying to use your gem but had a need to not consider some Exceptions as failure, i.e. using ActiveRecord to load a resource I can receive a 404 ResourceNotFoundException which isn't a failure, and shouldn't count as one.

I maked a change in your gem to be possible to pass an array with the exceptions which should not count as failures for circuit breaker.

I hope you can apply this to your gem.

Regards,
Wandenberg