[1.7.x] Fixed a typo in the admin documentation.
[1.7.x] Fixed a typo in the admin documentation.

The 'app' subpackage does not exist, should be 'app'.

Backport of b9daa4f0e1 from master

oscaro/django,oscaro/django,jyotsna1820/django,oscaro/django,jyotsna1820/django,oscaro/django,jyotsna1820/django,jyotsna1820/django