Log Message:
Update ruby-mixlib-config to 2.2.1.

2.2.1 (5/12/2015)

    * Rename key? back to has_key?

2.2.0 (5/11/2015)

    * Fix strict mode errors to print symbol (@jkeiser)
    * Pin rspec to version 2 (@sethvargo)
    * Move has_key? to key? for new-ruby happiness (@sethvargo)