Fix undefined 'bold' property (TypeError)

This fixes the undefined 'bold' property error when trying to generate a CommonJS module. 
I replaced the old welcome message banner inside `askFor()` to reference the new one provided by `yeoman-generator` (inside [lib/util/common.js](https://github.com/yeoman/generator/blob/master/lib/util/common.js)) through `welcome()`.

Cheers! :alien: