Switch README badges to SVG for hi-res funtimes
Switch README badges to SVG for hi-res funtimes

Also change from David to Gemnasium. We couldn't use it in the past
because we had a Gemfile, so it assumed this was a Ruby project. Now
it can tell that there's only JavaScript here.

alphagov/spotlight,keithiopia/spotlight,alphagov/spotlight,keithiopia/spotlight,alphagov/spotlight,tijmenb/spotlight,tijmenb/spotlight,tijmenb/spotlight,keithiopia/spotlight