Adding an MIT license

Guys, 

We're looking through our dependency list to see what licenses each of the things we bundle / have a transitive dependency on. 
We couldn't find a license for this particular project. I did see a few Heroku related projects being MIT and so have added PR to add the license.

Feel free to pick a difference license if you guys want but figured I'd do some leg work for you guys.
Let me know if you have any questions. 

Cheers,

Mark C