Travis build: openjdk8, openjdk11

[sullis]

No description provided.

[mikesamuel]

Why?

[sullis]

April 15, 2019: Ubuntu Xenial 16.04 as the default Travis CI build environment

link: https://blog.travis-ci.com/2019-04-15-xenial-default-build-environment

link: https://docs.travis-ci.com/user/reference/xenial/#differences-from-the-trusty-images

Pre-installed JVMs: openjdk8, openjdk10, and openjdk11

[sullis]

for reference:

-> Apache Zookeeper uses Travis-CI
-> Apache Zookeeper replaced OracleJDK with openjdk

link: apache/zookeeper#1005

link: apache/zookeeper@5e7d88b

[sullis]

Similar change in the [kotlinpoet] project:

square/kotlinpoet@6d6eed8

[mikesamuel]

Thanks for explaining.

[mikesamuel]

Thanks for the patch.

I pulled this locally, and switch to dist:trusty which https://docs.travis-ci.com/user/reference/trusty/#jvm-clojure-groovy-java-scala-images indicates has the widest range of available JVM versions.

I committed a version of your PR with my local edits.