Bug 1009198 - Add previous week data to Ouija wiki_update page.

History of revisions documented on https://bugzilla.mozilla.org/show_bug.cgi?id=1009198.
This should be:
request2.open('get', '/data/platform?platform='+android_version+'&startdate='+s_previous_week + '&enddate=' + s_last_week, true);