Fix copyright line in folly/synchronization/test/ParkingLotBenchmark.cpp

Summary: [Folly] Fix copyright line in `folly/synchronization/test/ParkingLotBenchmark.cpp`.

Reviewed By: andrewjcg

Differential Revision: D6758502

fbshipit-source-id: cae2a79940c7c9cc58c29977141199ab1e902081

folly/synchronization/test/ParkingLotBenchmark.cpp

 /*
- * Copyright 2017-present Facebook, Inc.
+ * Copyright 2018-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.