add oraclejdk8 early access build to travis

Add automated testing against oracle jdk8 to verify that owlapi compiles and tests all pass against it (without having to install it locally).

Travis-CI supports testing against the early access builds for jdk8 which are fairly stable now. Currently Travis is testing against build 117 which is only a few weeks old.

Tracking issue at travis-ci is:

https://github.com/travis-ci/travis-ci/issues/1330