cache-bust the rdlist.json file

[scottstanfield]

It's being aggressively cached by browsers. Do the same trick we use for CSS and JS files.

So rdlist.json will become 9e8ef00.rdlist.json. The SHA1 of the json file is pre-pended and the Gruntfile.js takes care of the references. Maybe. Might not work for files that aren't css and js.