Change the Google Analytics tracking code to follow openra.net

Followup of https://github.com/OpenRA/OpenRAWeb/issues/114 and https://github.com/OpenRA/OpenRAWeb/issues/109. Already deployed at https://github.com/OpenRA/openra.github.io/commit/8aee029fe2e3ca843f35dd4d8decfed6b7c18ff0. Tested it on https://www.google.com/analytics/web/#realtime/rt-overview/ This now makes it work properly.