cli: Trivial wording improvement of a comment

Change-Id: Ib569b39bdf0357c30c94c7a1b8d3ff87b811841c
Reviewed-on: http://review.gluster.org/7403
Reviewed-by: Justin Clift <justin@gluster.org>
Tested-by: Justin Clift <justin@gluster.org>
Reviewed-by: Anand Avati <avati@redhat.com>