[1.7.x] Fixed typo in middleware docs.
[1.7.x] Fixed typo in middleware docs.

Function definition should have an ending colon.

Backport of 48241ec9c4 from master

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