Update pep-html-template

Fixing links to PEPs sources from .txt to .rst (see python#431)

Author: Naereen

pep-html-template

@@ -21,7 +21,7 @@ to templates.  DO NOT USE THIS HTML FILE AS YOUR TEMPLATE!
 <td class="textlinks" align="left">
 [<b><a href="%(pyhome)s/">Python Home</a></b>]
 [<b><a href="%(pepindex)s">PEP Index</a></b>]
-[<b><a href="%(pephome)s/pep-%(pepnum)s.txt">PEP Source</a></b>]
+[<b><a href="%(pephome)s/pep-%(pepnum)s.rst">PEP Source</a></b>]
 </td></tr></table>
 %(body)s
 %(body_suffix)s