Add JDKs to Travis CI build

[remkop]

For example:

jdk:
  - oraclejdk8
  - oraclejdk11
  - oraclejdk-ea
  - openjdk8
  - openjdk9
  - openjdk10
  - openjdk11
  - openjdk-ea

https://docs.travis-ci.com/user/languages/java/#testing-against-multiple-jdks
https://sormuras.github.io/blog/2018-05-31-jdk-matrix.html
https://www.deps.co/guides/travis-ci-latest-java/

[remkop]

On Trusty, this works:

addons:
  apt:
    packages:
      - openjdk-6-jdk
jdk: openjdk6

https://docs.travis-ci.com/user/languages/java/#testing-against-multiple-jdks

[remkop]

Should be https://docs.travis-ci.com/user/reference/trusty/#jvm-clojure-groovy-java-scala-images

[remkop]

Jacoco 0.8.2 doesn’t support Java 13, so needs to be excluded when building on jdk > 12.

This SO answer may be a good way to accomplish this: https://stackoverflow.com/a/50032881/1446916