Also replace hash rockets in SLIM views

I like your fork of rip_hashrocket, but sadly it doesn't replace hash rockets in [SLIM](https://github.com/slim-template/slim) views.

My fork of your fork adds this functionality. Please merge and update [your pull request](https://github.com/workingBen/rip_hashrocket/pull/1) - maybe @workingBen will finally merge it sometime.