user-env-compile does not work

[kevinchiu]

From Heroku: user-env-compile has been deprecated and replaced by the ENV_DIR argument to buildpack compile scripts. Buildpacks maintained by Heroku have been updated to use this new argument by default to export the app’s the environment as needed during builds. Maintainers of 3rd party buildpacks in use by apps with user-env-compile enabled have been notified to make updates for this change.