Fixed #10009 -- Corrected a field reference in an example on rendering hidden...

Fixed #10009 -- Corrected a field reference in an example on rendering hidden fields. Thanks to karihre@gmail.com for the report.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@9862 bcc190cf-cafb-0310-a4f2-bffc1f526a37