[1.9.x] Fixed typo in docs/howto/deployment/wsgi/index.txt

WSGI servers obtain the path to the ``application`` callable from their

configuration. Django's built-in server, namely the :djadmin:`runserver`

command, read it from the :setting:`WSGI_APPLICATION` setting. By default, it's

command, reads it from the :setting:`WSGI_APPLICATION` setting. By default, it's

set to ``<project_name>.wsgi.application``, which points to the ``application``

callable in :file:`<project_name>/wsgi.py`.