fix some mixed space+tab indentation

This fixes all instances of " \t" in the code base. Most common case
seems to be after a "where" line; probably vim copied the two space layout
of that line.

Done as a background task while listening to episode 2 of the Type Theory
podcast.

Assistant/Threads/XMPPClient.hs

@@ -131,7 +131,7 @@ xmppClient urlrenderer d creds xmppuuid =
 		{- XEP-0199 says that the server will respond with either
 		 - a ping response or an error message. Either will
 		 - cause traffic, so good enough. -}
-	  	pingstanza = xmppPing selfjid
+		pingstanza = xmppPing selfjid
 
 	handlemsg selfjid (PresenceMessage p) = do
 		void $ inAssistant $