Fix config file syntax (hopefully).

.mention-bot

@@ -7,6 +7,5 @@
     "Misc/NEWS"
   ],
   "userBlacklist": ["gvanrossum"],
-  "userBlacklistForPR": ["benjaminp"],
-  "userBlacklistForPR": ["skrah"]
+  "userBlacklistForPR": ["benjaminp", "skrah"]
 }