examples/vweb: use map instead of string in call to app.json (#12338)

examples/vweb/vweb_example.v

@@ -26,7 +26,9 @@ fn main() {
 ['/users/:user']
 pub fn (mut app App) user_endpoint(user string) vweb.Result {
 	id := rand.intn(100)
-	return app.json('{"$user": $id}')
+	return app.json({
+		user: id
+	})
 }
 
 pub fn (mut app App) index() vweb.Result {