On 1/1/2017 two popular buildpacks authored by David Dollar (ddollar) -- heroku-buildpack-apt and heroku-buildpack-multi -- are set to expire, which means new builds using these buildpacks will fail.
Apt buildpack - github
This buildpack is used for installing packages from apt. As a replacement we suggest you use Herokus apt buildpack.
Multi buildpack - github
This buildpack is used for setting multiple buildpacks on an app. It is no longer necessary, as Heroku has native support for multiple buildpacks.
How do I add or remove a buildpack?
Learn more about adding and removing a buildpack.