Add JDK 9 compatibility and test

[tirkarthi]

• Since sun.boot.class.path and java.ext.dirs are removed on JDK 9 filter them for nil
• Add a test case

Fixes #24

[venantius]

Hm. This project doesn't seem to be hooked into a CI system, which is a bummer because ideally we'd get to check this test suite against both JDK 8 and JDK 9 on an ongoing basis. But since you've checked this on your computer in both cases hopefully that's good enough for now.

[tirkarthi]

Yes, adding a CI is pretty easy. Just got the commit checked with JDK 8 and JDK 9 on Travis CI

Build : https://travis-ci.org/tirkarthi/clojure-complete/builds/329454061

CI config : https://github.com/tirkarthi/clojure-complete/blob/137cffe2b157898d8799da5af6eef8aa8bceb6dd/.travis.yml

[ninjudd]

I no longer maintain this repository, but I'm happy to make either of you collaborators if you want to merge this or add CI integration. Just let me know.

[tirkarthi]

@ninjudd Thanks. I am afraid I am still a beginner with respect to Clojure ecosystem and have no experience with releases.

[venantius]

@ninjudd I'm afraid I've got a bit too much on my plate to be a "real" maintainer, but if you want to give me collaborator rights I can at least get CI set up and get this merged.

[ninjudd]

@venantius sounds good. I added you.