use ssh git urls for starters (#3690)
use ssh git urls for starters (#3690)

* use ssh git urls for starters

use `hosted-git-info`'s ssh url. This allows starters from private repos
to work while still supporting the defaults and public starters.

* Respect the string format that people passed in

ChristopherBiscardi/gatsby,0x80/gatsby,mingaldrichgan/gatsby,mingaldrichgan/gatsby,gatsbyjs/gatsby,0x80/gatsby,gatsbyjs/gatsby,fk/gatsby,mingaldrichgan/gatsby,ChristopherBiscardi/gatsby,0x80/gatsby,gatsbyjs/gatsby,ChristopherBiscardi/gatsby,fk/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,ChristopherBiscardi/gatsby,fk/gatsby,gatsbyjs/gatsby