(PDB-4140) travis: drop testing of oraclejdk >=8
(PDB-4140) travis: drop testing of oraclejdk >=8

Given that we're about to only test 8 and 11, and that as of at least
11 oraclejdk effectively is openjdk, stop testing oraclejdk for
versions newer than 8.

puppetlabs/puppetdb,puppetlabs/puppetdb,puppetlabs/puppetdb,puppetlabs/puppetdb,puppetlabs/puppetdb