Change effective on 27 June 2013
The Rubies for MRI on Heroku have been updated to 1.8.7-p374, 1.9.3-p448, and 2.0.0-p247. Upon next push to your Ruby app, you will recieve the updated Ruby. These are security releases, so we recommend updating your Ruby as soon as possible. As always, you can check the Ruby runtimes that are being deployed in the Heroku Ruby Support Article on Dev Center.