fix whitespace

Doc/library/itertools.rst

@@ -592,7 +592,7 @@ loops that truncate the stream.
 
    A common use for *repeat* is to supply a stream of constant values to *imap*
    or *zip*::
- 
+
       >>> list(imap(pow, range(10), repeat(2)))
       [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]