Fixed typo in Group module docstring.
Fixed typo in Group module docstring.

eternalfame/django-admin-tools,django-admin-tools/django-admin-tools,glowka/django-admin-tools,miurahr/django-admin-tools,glowka/django-admin-tools,miurahr/django-admin-tools,miurahr/django-admin-tools,django-admin-tools/django-admin-tools,eternalfame/django-admin-tools,miurahr/django-admin-tools,glowka/django-admin-tools,django-admin-tools/django-admin-tools,eternalfame/django-admin-tools