install.sh (get.docker.io) aufs comment updated.

devicemapper has landed, but the TODO hasn't been actioned presumably
because aufs is still preferred over devicemapper when available[1].

Comment updated accordingly.

Citation [1]: https://github.com/crosbymichael/docker/blob/267ca39921c35826ccbdb84fbbc0690bfef385d7/runtime/graphdriver/driver.go#L40-L46

Docker-DCO-1.1-Signed-off-by: Paul Annesley <paul@annesley.cc> (github: pda)
Upstream-commit: 576278102e0fa9166711f8cf23ec972fcccc085e
Component: engine

components/engine/hack/install.sh

@@ -85,7 +85,7 @@ case "$lsb_dist" in
 			fi
 		}
 		
-		# TODO remove this section once device-mapper lands
+		# aufs is preferred over devicemapper; try to ensure the driver is available.
 		if ! grep -q aufs /proc/filesystems && ! $sh_c 'modprobe aufs'; then
 			kern_extras="linux-image-extra-$(uname -r)"