Make the server executable

bin/customs_server.js

@@ -1,3 +1,5 @@
+#!/usr/bin/env node
+
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */