ci(travis): bump macOS to 10.13 
ci(travis): bump macOS to 10.13 

and remove openJDK11 since its now on appveyor

RemiKoutcherawy/exist,RemiKoutcherawy/exist,RemiKoutcherawy/exist,RemiKoutcherawy/exist,RemiKoutcherawy/exist,RemiKoutcherawy/exist