[video_player] fix license header

packages/video_player/video_player_platform_interface/test/video_player_options_test.dart

@@ -1,3 +1,7 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
 import 'package:flutter_test/flutter_test.dart';
 import 'package:video_player_platform_interface/video_player_platform_interface.dart';