resize x86 rootfs to 36 MB and kernel to 16 MB

This will allow x86 devices with 256 MB disk to upgrade.
3 jobs for v2018.2.3-ffs in 2 minutes and 11 seconds (queued for 2 seconds)
Name Stage Failure
build Build
Step 4/11 : ENV USER=herokuishuser
---> Running in 9aaaa34ab0a3
Removing intermediate container 9aaaa34ab0a3
---> 43f38f117c2e
Step 5/11 : RUN /bin/herokuish buildpack build
---> Running in 670c64a4d613
-----> Unable to select a buildpack
The command '/bin/sh -c /bin/herokuish buildpack build' returned a non-zero code: 1
ERROR: Job failed: exit code 1