One more Fix java8

One more proposition java8 Fix. I saw that you have already tried to use new eclipse jdt (org.eclipse.tycho). But, I don't know why you revert this changes. Now I have a build with this changes in my orika-fork https://github.com/jad7/orika/ and you can see, that my Travis build is a green https://travis-ci.org/jad7/orika/ with this changes on jdk7 and jdk8. I think, it's should fix main build.