Fix license headers

Reviewed By: scottrice

Differential Revision: D17673481

fbshipit-source-id: 1794e0a6e92e6894b5634b24c6e7910847616261

iOS/Plugins/FlipperKitUserDefaultsPlugin/FKUserDefaultsPlugin.m

@@ -1,3 +1,9 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the LICENSE
+ * file in the root directory of this source tree.
+ */
 //
 //  FKUserDefaultsPlugin.m
 //  Sample