docs(copyright): correct name of company for commits after 2015 (#440)

diff --git a/google/auth/_oauth2client.py b/google/auth/_oauth2client.py
index b14a382..95a9876 100644
--- a/google/auth/_oauth2client.py
+++ b/google/auth/_oauth2client.py
@@ -1,4 +1,4 @@
-# Copyright 2016 Google Inc.
+# Copyright 2016 Google LLC
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.