Fixed #18257 -- Typo in contenttypes docs.

is implemented, you cannot use such fields directly with filters (``filter()``

and ``exclude()``, for example) via the database API. Because a

:class:`~django.contrib.contenttypes.generic.GenericForeignKey` isn't a

normal field objects, these examples will *not* work::

normal field object, these examples will *not* work::

    # This will fail

    >>> TaggedItem.objects.filter(content_object=guido)