alas, in version 0.11, still some parts are not Java 8 compatible: kc/mega/game/Battleffield has been compiled by version 57.0.
Does not matter that much, I am just not able (currently) to run any battles for it. Same for Raven as it has been compiled by version 55.0.
Oops, I will have another go at fixing it for my next release!
I've downloaded Java 13, I can now run battles for BeepBoop. After rebuilding the robot-database, also Raven and WaveShark run fine. Note that for my development I will still use the compiler option '-source 1.8'