Update menu_item.html

The template tags library adminmedia, which only contained the deprecated template tag {% admin_media_prefix %}, was removed. Attempting to load it with {% load adminmedia %} will fail. If your templates still contain that line you must remove it.
https://docs.djangoproject.com/en/1.5/releases/1.5/#miscellaneous
Merge pull request #83 from AntonioReyes/patch-3

Removed adminmedia load from menu_item.html