Fix copyright lines in folly/synchronization/Baton.h

Summary: [Folly] Fix copyright lines in `folly/synchronization/Baton.h`.

Reviewed By: meyering

Differential Revision: D6665595

fbshipit-source-id: 84aa0c475f01c858d543a047103437c083b3a4ed

folly/synchronization/Baton.h

 /*
- * Copyright 2017 Facebook, Inc.
+ * Copyright 2014-present Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.

folly/synchronization/test/BatonBenchmark.cpp

 /*
- * Copyright 2017 Facebook, Inc.
+ * Copyright 2016-present Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.

folly/synchronization/test/BatonTest.cpp

 /*
- * Copyright 2017 Facebook, Inc.
+ * Copyright 2014-present Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.

folly/synchronization/test/BatonTestHelpers.h

 /*
- * Copyright 2017 Facebook, Inc.
+ * Copyright 2016-present Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.