Copyright (#8970)

* Add copyright everywhere missing

* Style

tests/test_modeling_transfo_xl.py

@@ -1,5 +1,5 @@
 # coding=utf-8
-# Copyright 2018 The Google AI Language Team Authors.
+# Copyright 2020 The HuggingFace Team. All rights reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -12,6 +12,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+
 import copy
 import random
 import unittest