Sets release date for 3.1 to Thursday

Changelog

@@ -12,7 +12,7 @@ new in Celery 3.1.
 
 3.1.0
 =======
-:release-date: 2013-11-01 XX:XX X.X BST
+:release-date: 2013-11-07 XX:XX X.X UTC
 :state: FROZEN
 
 See :ref:`whatsnew-3.1`.