Add Travis-CI config

You'll need to create a travis-ci.org account and enable travis for this repo, but this config should be sufficient to make travis run the test suite and report any errors after each batch of commits that is pushed. Once that's setup you can add a badge to the README too.

You may not be interested in rubinius and jruby, but figured might as well include them and help those ecosystems gather wider support. Surprisingly, it's not the other VMs that have an issue, but merry Xmas, [Ruby 2.2.0 doesn't like the latest build](https://travis-ci.org/tdg5/directory_monitor/builds/45149490), so that's something to look into.