Ruby 2.2.0 & Rails 4.2.0 app push fail

gistfile1.txt

-----> Fetching custom tar buildpack... done
-----> Ruby app detected
-----> Compiling Ruby/Rails
 !
 !     Command: 'set -o pipefail; curl --fail --retry 3 --retry-delay 1 --connect-timeout 3 --max-time 20 https://s3-external-1.amazonaws.com/heroku-buildpack-ruby/ruby-2.2.0.tgz -s -o - | tar zxf -' failed unexpectedly:
 !     
 !     gzip: stdin: unexpected end of file
 !     tar: Child returned status 1
 !     tar: Exiting with failure status due to previous errors
 !

 !     Push rejected, failed to compile Ruby app

If this happens to you it means you're probably using a custom buildpack and forgot about it. I did.

Check heroku config for your app, there should be a BUILDPACK_URL set, which is the telltale for a custom buildpack. To remove it, simply unset that environment variable with:

heroku config:unset BUILDPACK_URL

And off you go. 😃

PS: Thanks to @hone (Terence Lee) for the help fixing that.