fix error when project yaml file has no deprecation

When project yaml file has no deprecations, upon starting it with tmuxinator, an error is thrown.
![by default 2013-07-25 at 8 56 17 am](https://f.cloud.github.com/assets/43447/853165/a65c5c30-f4ce-11e2-9ee0-0f781d96c6f4.png)