init help: update generator listing

If the generator have only one sub generator it will group into previous generator 
Example : 

```
Backbone
  backbone:all
  backbone:app
  backbone:collection
  backbone:model
  backbone:router
  backbone:view
  chrome-extension:app
  ember:all
  jasmine:app
```
This PR will update this into

```
Backbone
  backbone:all
  backbone:app
  backbone:collection
  backbone:model
  backbone:router
  backbone:view

Chrome-extension
  chrome-extension:app

Ember
  ember:all

Jasmine
  jasmine:app
```