fix header

Author: jacksonrl

pkgs/ffigen/lib/src/header_parser/sub_parsers/var_parser.dart

@@ -1,3 +1,7 @@
+// Copyright (c) 2021, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
 import '../../code_generator.dart';
 import '../../config_provider/config.dart';
 import '../../config_provider/config_types.dart';