WIP - Update Travis CI to use JDK 11

[mmoayyed]

Let Travis CI use JDK 11.

This will likely not pass for a number of iterations, and for a while until all underlying libraries have had a chance to catch up. Will get the pull updated periodically to ensure correctness before the final merge.

/remind me to review this again once JDK 11 is released in 3 days

See gradle/gradle#5120 (comment)

[stale]

This patch has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[mmoayyed]

Pending https://issues.apache.org/jira/browse/GROOVY-8727

[GROOVY-8727] JDK 11 Compilation Failure: ClassVisitor.visitNestMemberExperimental throws UnsupportedOperationException - ASF JIRA

[stale]

This patch has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@21b4189). Click here to learn what that means.
The diff coverage is n/a.

@@           Coverage Diff            @@
##             master   #3406   +/-   ##
========================================
  Coverage          ?      0%           
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  Files             ?    1413           
  Lines             ?   30330           
  Branches          ?    2828           
========================================
  Hits              ?       0           
  Misses            ?   30330           
  Partials          ?       0

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