text: Title: Goin' Fast URL IPv6 address is not bracketed
  Body: Sanic says:
  ```
  sanic myprogram.app -H ::
  Goin' Fast @ http://:::8000
  ```
  
  The correct formatting for IPv6 would be:
  ```
  Goin' Fast @ http://[::]:8000
  ```
  
  Fixing the Goin' fast banner in `sanic/app.py` would be an easy enough task for someone wishing to start hacking Sanic. Existing code from `sanic/models/server_types.py` class `ConnInfo` could be useful, as there already is handling for adding brackets to IPv6 addresses.
  