Add missing storage drivers to bash completion

Signed-off-by: Harald Albers <github@albersweb.de>

contrib/completion/bash/docker

@@ -512,7 +512,7 @@ _docker_daemon() {
 			return
 			;;
 		--storage-driver|-s)
-			COMPREPLY=( $( compgen -W "aufs devicemapper btrfs overlay" -- "$(echo $cur | tr '[:upper:]' '[:lower:]')" ) )
+			COMPREPLY=( $( compgen -W "aufs btrfs devicemapper overlay vfs zfs" -- "$(echo $cur | tr '[:upper:]' '[:lower:]')" ) )
 			return
 			;;
 		--log-level|-l)