Prepare for new Yeoman Generator prompt()s.

RE: https://github.com/yeoman/generator/pull/250

Same idea as: https://github.com/Thomas-Lebeau/generator-jekyll/pull/2 :)

The Yeoman Generator has implemented a new prompt library, and as the release is imminent. See the above link, as well as [Inquirer](https://github.com/SBoudrias/Inquirer.js), to see the new library.

This PR should make the transition seamless :)