webupd8teams's JDK 8 installer PPA has been discontinued. Travis ci fails

[Ryan-Bell]

The travis ci install script fails with:

Package oracle-java8-installer is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or is only available from another source
E: Package 'oracle-java8-installer' has no installation candidate

As per https://launchpad.net/~webupd8team/+archive/ubuntu/java it seems this PPA was discontinued in April.

I ran the the travis build with only sudo apt update && sudo apt install maven and the tests worked.
If you're okay with removing these lines I can open a PR that will get the CI working