Change effective on 06 July 2018
The Heroku-16, and Heroku-18 stacks have been updated 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.
This update also adds new packages:
libseccomp-devon Heroku-16 and Heroku-18 (available at build time only)
libargon2-0-devon Heroku-18 (available at build time only)
The Ubuntu Packages on Heroku Stacks article contains a list of packages available on the Cedar-14, Heroku-16, and Heroku-18 stacks.