init help: update generator listing

[revathskumar]

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

[sindresorhus]

Thanks 🍰