Update trainer_lib.py (#1556)
Update trainer_lib.py (#1556)

Fixes #1299.

Signed-off-by: Bairen Yi <442ca6ae4fc71d92d014371455a9032c4a250bed@connect.ust.hk>
tensorflow/tensor2tensor,tensorflow/tensor2tensor,tensorflow/tensor2tensor,tensorflow/tensor2tensor,tensorflow/tensor2tensor