fix ptb author name bug (#2858)

* fix ptb author bug; test=develop

* fix ptb author bug; test=develop

dygraph/ptb_lm/reader.py

-# Copyright 2015 The TensorFlow Authors. All Rights Reserved.
+# Copyright (c) 2019 PaddlePaddle Authors. 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.
@@ -11,8 +11,7 @@
 # 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.
-# ==============================================================================
-"""Utilities for parsing PTB text files."""
+
 from __future__ import absolute_import
 from __future__ import division
 from __future__ import print_function