Display generator versions in `yo yo`

Fixes #39

This is how it looks:

![screenshot from 2013-07-05 23 06 47](https://f.cloud.github.com/assets/9906/755603/303d5f70-e5b7-11e2-9753-7595d3e40b77.png)

@stephenplusplus Could you review this and give your opinion? I'm not sure the way I modified the test is the best.