Update ruby to 2.1.2

I've also updated two gems that weren't working anymore with ruby 2.1.2:

- therubyracer
- newrelic_rpm

Updating newrelic_rpm also solved another problem:

![screenshot 2014-06-20 09 46 25](https://cloud.githubusercontent.com/assets/151725/3338183/5edc549a-f857-11e3-8f66-4f3e8b6f190b.png)

Could this be related to https://github.com/potomak/tomatoes/issues/113 ?