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 <[email protected]>
Run-TryBot: Heschi Kreinick <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
TryBot-Result: Go Bot <[email protected]>

Author: heschi

http2/h2demo/Makefile

@@ -26,7 +26,7 @@ push-prod: docker
 
 # 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)