[1.7.x] Fixed typo in docs/ref/contrib/gis/geos.txt.
[1.7.x] Fixed typo in docs/ref/contrib/gis/geos.txt.

Backport of fef26e9a87 from master

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