Fix range for go 1.3

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

api/client/utils.go

@@ -260,7 +260,7 @@ func (cli *DockerCli) monitorTtySize(id string, isExec bool) error {
 	sigchan := make(chan os.Signal, 1)
 	gosignal.Notify(sigchan, signal.SIGWINCH)
 	go func() {
-		for range sigchan {
+		for _ = range sigchan {
 			cli.resizeTty(id, isExec)
 		}
 	}()