fix formatting in last code snippet.

docs/streaming_how_to.rst

@@ -100,7 +100,7 @@ in a window of time, they will receive error 420.  The amount of time a client h
 will increase exponentially each time they make a failed attempt. 
 
 Tweepy's **Stream Listener** usefully passes error messages to an **on_error** stub. We can use **on_error** to 
-catch 420 errors and disconnect our stream.::
+catch 420 errors and disconnect our stream. ::
 
   class MyStreamListener(tweepy.StreamListener):