Fixed #9059: Corrected some markup in tutorial 4 that incorrectly identified a...

Fixed #9059: Corrected some markup in tutorial 4 that incorrectly identified a template variable as a function. Thanks to zen for the report.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@9022 bcc190cf-cafb-0310-a4f2-bffc1f526a37