don't use circleCI url in the "fiddle" link in autocomments

[hellochar]

when you click "fiddle" in the autocomment bot, the resultant fiddle uses links to circle CI urls - e.g. //710-16149854-gh.circle-artifacts.com/0/home/ubuntu/plottable/plottable.js

This will fail for most users since the link requires auth into circleCI to be accessible.