Update admin_distributed_geo_rep.md

Fixed typo

Change-Id: If4281237394ed96b32ec2d6227827214908052cf
Signed-off-by: Justin Clift <justin@gluster.org>
Reviewed-on: http://review.gluster.org/9268
Reviewed-by: M S Vishwanath Bhat <vbhat@redhat.com>
Reviewed-by: Humble Devassy Chirammal <humble.devassy@gmail.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>