cmd/sketch: make -open default to true
diff --git a/dockerimg/dockerimg.go b/dockerimg/dockerimg.go
index 150fcf8..9ca188b 100644
--- a/dockerimg/dockerimg.go
+++ b/dockerimg/dockerimg.go
@@ -446,6 +446,7 @@
 		"-outside-hostname="+config.OutsideHostname,
 		"-outside-os="+config.OutsideOS,
 		"-outside-working-dir="+config.OutsideWorkingDir,
+		"-open=false",
 	)
 	if config.SkabandAddr != "" {
 		cmdArgs = append(cmdArgs, "-skaband-addr="+config.SkabandAddr)