Travis: Build and test on JDK 7, 8 and 11.
Travis: Build and test on JDK 7, 8 and 11.

This uses the Trusty (14.04) image since that in the only one
where all three JDKs are available.

fzs/gitblit,fzs/gitblit,mystygage/gitblit,mystygage/gitblit,fzs/gitblit,fzs/gitblit,mystygage/gitblit,gitblit/gitblit,fzs/gitblit,gitblit/gitblit,gitblit/gitblit,mystygage/gitblit,mystygage/gitblit,gitblit/gitblit,gitblit/gitblit