Update Apache header according to go/releasing/preparing

https://opensource.google.com/docs/releasing/preparing/#include-license-file-and-source-code-headers

Author: ia0

README.md

@@ -36,7 +36,7 @@ doesn't comply with the license.)
 
 Apache header:
 
-    Copyright 2018 Google Inc.
+    Copyright 2018 Google LLC
 
     Licensed under the Apache License, Version 2.0 (the "License");
     you may not use this file except in compliance with the License.