Enable Travis CI

[jimklimov]

@kohsuke : now that .travis.yml file is here, you as the repo owner should enable the builds.

Log in to https://travis-ci.org (there's a button to use your GitHub account as the Travis account), tell it to watch your repos, and enable the slider to build for this one. Then upon the next commit or PR, it will auto-test. Take note to give a similar service (or perhaps better - e.g. more multiplatform) with a Jenkins cloud, so as to not lose ground to competitiors :)

For details see https://docs.travis-ci.com/user/getting-started/

[jimklimov]

Addressed even better via establishment of https://ci.jenkins.io/job/Libraries/job/libzfs4j/ job