[1.3.X] Fixed #17757 - Typo in docs/intro/overview.txt; thanks kaushik1618.

Backport of r17584 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.3.X@17585 bcc190cf-cafb-0310-a4f2-bffc1f526a37