corrected copyright header in gentest.js

Summary:
@public

We have changed Yoga’s license to a yearless format, but this was not reflected in the test generation script.
This commit changes the corresponding template/.

Reviewed By: davidaurelio

Differential Revision: D10852787

fbshipit-source-id: 0b79e253be6174a218f9dc8de942fc2496a425c8

gentest/gentest.js

@@ -42,7 +42,7 @@ function assert(condition, message) {
 function printTest(e, LTRContainer, RTLContainer, genericContainer) {
   e.push([
     '/**',
-    ' * Copyright (c) 2014-present, Facebook, Inc.',
+    ' * 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.',