Fixed ReST error in [2332]

git-svn-id: http://code.djangoproject.com/svn/django/trunk@2333 bcc190cf-cafb-0310-a4f2-bffc1f526a37

docs/outputting_pdf.txt

@@ -135,7 +135,7 @@ efficient. Here's the above "Hello World" example rewritten to use
         response.write(pdf)
         return response
 
-.. cStringIO: http://www.python.org/doc/current/lib/module-cStringIO.html
+.. _cStringIO: http://www.python.org/doc/current/lib/module-cStringIO.html
 
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