change how APP_URL is used, use JS templating string

app/config/appConfig.js

@@ -0,0 +1,9 @@
+const APP_PORT = process.env.APP_PORT || 5000;
+const APP_BASE_URL = process.env.APP_BASE_URL || "http://localhost";
+
+const APP_URL = `${APP_BASE_URL}:${APP_PORT}`;
+
+module.exports = {
+  APP_PORT,
+  APP_URL
+};