rails_12factor gem

The logs weren't showing anything useful. I added the 12 factor gem, which is something you should do for all Rails apps on Heroku, and then the logs showed this:

![2014-07-28 at 9 45 pm](https://cloud.githubusercontent.com/assets/181187/3730523/d73beeba-16d3-11e4-9130-28de8aa47173.png)

That means that migrations needed to be run with `heroku run rake db:migrate`.

I also set the Ruby version, which is important but wasn't the problem.