Add API_SECRET to Heroku deployment

Simplifies deploying a Heroku app by adding the API_SECRET var to the app deployment.

![screen shot 2014-11-19 at 6 53 46 pm](https://cloud.githubusercontent.com/assets/6069420/5118902/b55e0dac-701d-11e4-8cd5-aec9b39f5ae6.png)