Add simple openjdk11 jobs on Travis CI
Add simple openjdk11 jobs on Travis CI

Integration tests aren't run in particular, nor tests relying on the
proguarded CLI

coursier/coursier,coursier/coursier,alexarchambault/coursier,alexarchambault/coursier,alexarchambault/coursier,coursier/coursier,coursier/coursier,alexarchambault/coursier