Add Python 3.7, 3.8 and openjdk>8 to build matrix

[StephenBrown2]

Per #369 (comment) , Python 3.6 is already tested, however #369 states:

the Python module does not work in Python 3.7

So, adding python 3.7 and 3.8, which have some potentially breaking changes, to the build matrix for continuous testing.

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[zongweil]

What's prompting this change? We currently have the dist set to trusty globally - do Python 3.7 and 3.8 need to specifically run with bionic?

[StephenBrown2]

Yes, trusty does not support python 3.7 or 3.8. The Travis build for the first commit failed on Python 3.7 and on Python 3.8 with the reason: Unable to download 3.(7|8) archive. The archive may not exist. Please consider a different version.

[zongweil]

Got it, thanks for the clarification. Would you mind setting the global dist to bionic and seeing if everything still passes? I'd prefer to keep everything in sync if possible.

[StephenBrown2]

Will do. 👍

[StephenBrown2]

It appears that Java 8 is no longer available on bionic, as it is EOL. Can bump the dist down to xenial, or set it specifically for java8 and add later jdks to be sure they work as well.

[zongweil]

I like your second approach - let's default to bionic and set it to older dist versions as needed. Thanks for doing this!

[StephenBrown2]

It appears that the java build has problems with newer jdks, specifically with javadoc in jdk11+, and oraclejdk10 quit with a deprecated message, so I've removed all non-LTS Oracle JDKs from the test matrix.

This still leaves the failures for jdk11+, so shall I comment those out, or allow them to fail?

[zongweil]

This still leaves the failures for jdk11+, so shall I comment those out, or allow them to fail?

Feel free to comment them out for now. I'll merge in the PR once done.

[StephenBrown2]

rubocop still failing as it has from the start, though everything else is green.