Travis: Add Java 12 build (openjdk-ea is now Java 13).
Travis: Add Java 12 build (openjdk-ea is now Java 13).

flowable/flowable-engine,yvoswillens/flowable-engine,dbmalkovsky/flowable-engine,yvoswillens/flowable-engine,paulstapleton/flowable-engine,paulstapleton/flowable-engine,dbmalkovsky/flowable-engine,flowable/flowable-engine,flowable/flowable-engine,paulstapleton/flowable-engine,yvoswillens/flowable-engine,paulstapleton/flowable-engine,dbmalkovsky/flowable-engine,yvoswillens/flowable-engine,flowable/flowable-engine,dbmalkovsky/flowable-engine