http2/h2demo: set prod namespace for deploy

Forgot to do this.

Change-Id: I74a4f53047c99825005d323b6c70d4215e5cb8ea
Reviewed-on: https://go-review.googlesource.com/c/net/+/348589
Trust: Heschi Kreinick <heschi@google.com>
Run-TryBot: Heschi Kreinick <heschi@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
diff --git a/http2/h2demo/Makefile b/http2/h2demo/Makefile
index d12d1b4..ceeb9bc 100644
--- a/http2/h2demo/Makefile
+++ b/http2/h2demo/Makefile
@@ -26,7 +26,7 @@
 
 # TODO(bradfitz): add REPO subsitution in xb for the kubectl command.
 deploy-prod: push-prod
-	xb --prod kubectl set image deployment/h2demo-deployment h2demo=gcr.io/symbolic-datum-552/h2demo:$(VERSION)
+	xb --prod kubectl --namespace prod set image deployment/h2demo-deployment h2demo=gcr.io/symbolic-datum-552/h2demo:$(VERSION)
 deploy-staging: push-staging
 	xb --staging kubectl set image deployment/h2demo-deployment h2demo=gcr.io/go-dashboard-dev/h2demo:$(VERSION)