travis: dropping Python 3 CI
travis: dropping Python 3 CI

Former-commit-id: c9838599c4ab7f995581b164d61d8b9f6a4ec5ab
Mindwerks/worldengine,tmfoltz/worldengine,esampson/worldengine,Mindwerks/worldengine,esampson/worldengine,psi29a/worldengine,MM1nd/worldengine,tmfoltz/worldengine,MM1nd/worldengine,sylvanmist/worldengine,sylvanmist/worldengine,psi29a/worldengine