Add linebreak to docstring to fix markup and silence Sphinx waraning.

Without the added linebreak the line of ----- is treated as heading
markup for the line below, and it is broken markup because it is an
overline without an underline.
With the added linebreak the line of ------ is rendered as an hr element
and the line below is also rendered.

IPython/utils/tokenize2.py

@@ -13,6 +13,7 b' Patches:'
 - u and rb literals are allowed under Python 3.3 and above.
 
 ------------------------------------------------------------------------------
+
 Tokenization help for Python programs.
 
 tokenize(readline) is a generator that breaks a stream of bytes into