builder/services.go: Update proxyd flag

Required change to match
https://vanadium-review.googlesource.com/#/c/5330/

MultiPart: 2/2
Change-Id: Ifd108947764c20a9a2c43596cb8461637efb5eb1
diff --git a/go/src/playground/builder/services.go b/go/src/playground/builder/services.go
index 00dc9a6..019d32f 100644
--- a/go/src/playground/builder/services.go
+++ b/go/src/playground/builder/services.go
@@ -50,8 +50,7 @@
 		"proxyd",
 		"-log_dir=/tmp/logs",
 		"-name="+proxyName,
-		"-address=127.0.0.1:0",
-		"-http=")
+		"-veyron.tcp.address=127.0.0.1:0")
 	if _, err := startAndWaitFor(cmd, timeLimit, regexp.MustCompile("NAME=(.*)")); err != nil {
 		return nil, fmt.Errorf("Error starting proxy: %v", err)
 	}