Fix compilation on Go 1.3.3

Docker-DCO-1.1-Signed-off-by: Jessie Frazelle <jess@docker.com> (github: jfrazelle)

api/client/commands.go

@@ -2728,7 +2728,7 @@ func (cli *DockerCli) CmdStats(args ...string) error {
 	if len(errs) > 0 {
 		return fmt.Errorf("%s", strings.Join(errs, ", "))
 	}
-	for range time.Tick(500 * time.Millisecond) {
+	for _ = range time.Tick(500 * time.Millisecond) {
 		printHeader()
 		toRemove := []int{}
 		for i, s := range cStats {