chat: Change vomtestgen and vdl tools flags from underscores to hyphens.

MultiPart: 4/6

Change-Id: Ib09b1a2b6ff3c53d96154670c79012a8ef7ffd74
diff --git a/Makefile b/Makefile
index 3b9ea40..c26dd67 100644
--- a/Makefile
+++ b/Makefile
@@ -131,7 +131,7 @@
 
 gen-vdl: vanadium-binaries
 	vdl generate --lang=go chat/vdl
-	vdl generate --lang=javascript --js_out_dir=clients/web/js chat/vdl
+	vdl generate --lang=javascript --js-out-dir=clients/web/js chat/vdl
 
 clients/shell/src/github.com/fatih/color:
 	$(GO) get github.com/fatih/color