refs mapbox/geojson.io#346 -- extract owner login

refs: mapbox/geojson.io#346

It looked like the ``d.user`` property was null. By inspecting the ``d`` variable, I've found that there was an ``owner`` property that was associated to the gist owner.

I have no mean to test this patch, but I hope it'd fix this.
Rebuild
Merge branch 'brunobord-gh-pages' into gh-pages