drop Node.js v0.4.x testing

Travis CI does not perform Node.js v0.4.x testing ([example](https://travis-ci.org/visionmedia/commander.js/jobs/24533952)), and thus the corresponding line in `.travis.yml` is redundant. It's just too old, that Node's version.

**P. S. ** And while I am at it, let's start testing in newer Node.js versions (0.8.x and 0.10.x).