Add recipe-tester.com support

Hey Brian,

This adds a configuration file for [Recipe Tester](https://www.recipe-tester.com). Recipe Tester is a hosted continuous integration system for Chef cookbooks. It's like Travis-CI, but for Chef cookbooks.

You'll also need to add a Github post-receive hook for this to work. More info in the [docs](http://docs.recipe-tester.com/).

The build that my fork is running on can be found [here](https://www.recipe-tester.com/repo/spulec/redisio/).