Update prod.dart

bin/prod.dart

@@ -23,6 +23,7 @@ void isolateMain(int id) {
   app.configure(configureServer).then((_) async {
     // In production, we'll want to log errors to a file.
     // Alternatives include sending logs to a service like Sentry.
+    hierarchicalLoggingEnabled = true;
     app.logger = new Logger('angel')
       ..onRecord.listen((rec) {
         if (rec.error == null) {