travis: update config
travis: update config

- cleanup default jobs
- add a target-level=11 job
- fix JDK versions on MacOS VMs
- disable windows builds for now, as they seem to break if the repo has secrets env variables

LearnLib/automatalib,LearnLib/automatalib,LearnLib/automatalib,misberner/automatalib,LearnLib/automatalib,misberner/automatalib