Add Foodcritic lint checks

> [Foodcritic](http://www.foodcritic.io/) is a helpful lint tool you can use to check your Chef cookbooks for common problems.
>
> It comes with 47 built-in rules that identify problems ranging from simple style inconsistencies to difficult to diagnose issues that will hurt in production.

This is one of at least two automated tests I want to add to the Practicing Ruby cookbook (the other one being integration tests).