upgrade to the latest buildpack

[duanhongyi]

No description provided.

[Cryptophobia]

Hi @duanhongyi , thank you very much for the awesome contribution! Just a couple of things:

1. Can you modify the commit messages so they fit our commit-style?
   https://docs.teamhephy.com/contributing/submitting-a-pull-request/#commit-style

2. Can you rebase from master or merge in master on top of your branch so that travis CI run? I just pushed a commit to master that is supposed to fix travis CI.

Also, do you know of a good way that we can write a test to build slugs for all of these buildpacks and verify that they run correctly? Not sure if this is something we want to do as it will be a time consuming test but it might be good to run as an integration test every once in a while...

[duanhongyi]

OK, I try to upgrade to heroku-18 and submit it all together.

[Cryptophobia]

@duanhongyi , that would be great! Let me know if you need any assistance.

[kingdonb]

Also, do you know of a good way that we can write a test to build slugs for all of these buildpacks and verify that they run correctly?

That's definitely a feature of the jenkins-jobs "e2e-runner"

Maybe it's time to resurrect that effort, so we can say we've done e2e testing on the next release and report on the results. (I think it would be good to say all the tests are passing, but knowing how bitrot works, I think we've probably got a lot of work ahead of us to get to that point.)

teamhephy/jenkins-jobs@2bcd75f This commit says that's what it does (test all the buildpacks), but there are enough layers of indirection between jenkins-jobs, e2e-runner, workflow-dev-e2e, etc. that I haven't been able to find a list of buildpacks, or some place where they were enumerated.

I've only given it a cursory glance at this point though, so I wouldn't doubt that it's in there...

[kingdonb]

Actually, here this looks like the place: https://github.com/teamhephy/workflow-e2e/blob/master/tests/buildpacks_test.go