Fix mobile redirect breakage

Commit Iebfbc46 broke the mobile redirect for mediawiki.org,
wikimediafoundation.org and wikimedia.org subdomains. Fortunately it was
caught very shortly after its deployment and affects a very minor amount
of traffic. Fix this by fixing the regsubs().

Change-Id: I977c3bd04a0b5573efb88774fa6090e5e6f106f8