Change effective on 17 October 2017
The Heroku Cedar-14 stack image has been updated with the most recent versions of installed packages to address a Ruby security vulnerability.
The new stack image will be rolled out automatically in the next 24 hours. You do not need to redeploy your app or restart your dynos.
See this Dev Center article for an overview of the libraries available on the Cedar-14 and Heroku-16 stack images.