Reminder: Pull request CI checks will break on May 1

[Ryan Schmidt]

The Bintray service will cease to exist on May 1. Our pull request CI checks rely on being able to download certain assets from Bintray, so unless we do something to fix this before then, our pull request CI checks will no longer work as of May 1.

https://jfrog.com/blog/into-the-sunset-bintray-jcenter-gocenter-and-chartcenter/