Change effective on 23 July 2019
This update has been rolled back for all stacks due to incompatibilities between the updated dependencies and some vendor/library combinations.
We have updated the Cedar-14, Heroku-16, and Heroku-18 stack images to address security notices in multiple packages. The new stack images 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, Heroku-16, and Heroku-18 stack images.