Update `.travis.yml`
Update `.travis.yml`

* Start using Travis CI's container-based infrastructure.
  http://docs.travis-ci.com/user/workers/container-based-infrastructure/

* Add `io.js` runtime.
  https://iojs.org/

* Update `Node.js` to `v0.12.0`.

Closes #19.

mathiasbynens/node-unicode-data,mathiasbynens/node-unicode-data