Error on dtype in modeling_bertabs.py file
# 🐛 Bug

Traceback (most recent call last):
  File "run_summarizationn.py", line 324, in <module>
    main()
  File "run_summarizationn.py", line 309, in main
    evaluate(args)
  File "run_summarizationn.py", line 84, in evaluate
    batch_data = predictor.translate_batch(batch)
  File "/kaggle/working/transformers/examples/summarization/bertabs/modeling_bertabs.py", line 797, in translate_batch
    return self._fast_translate_batch(batch, self.max_length, min_length=self.min_length)
  File "/kaggle/working/transformers/examples/summarization/bertabs/modeling_bertabs.py", line 844, in _fast_translate_batch
    dec_out, dec_states = self.model.decoder(decoder_input, src_features, dec_states, step=step)
  File "/opt/conda/lib/python3.6/site-packages/torch/nn/modules/module.py", line 547, in __call__
    result = self.forward(*input, **kwargs)
  File "/kaggle/working/transformers/examples/summarization/bertabs/modeling_bertabs.py", line 231, in forward
    step=step,
  File "/opt/conda/lib/python3.6/site-packages/torch/nn/modules/module.py", line 547, in __call__
    result = self.forward(*input, **kwargs)
  File "/kaggle/working/transformers/examples/summarization/bertabs/modeling_bertabs.py", line 328, in forward
    dec_mask = torch.gt(tgt_pad_mask + self.mask[:, : tgt_pad_mask.size(1), : tgt_pad_mask.size(1)], 0)
RuntimeError: expected device cpu and dtype Byte but got device cpu and dtype Bool

## Information

Model I am using (Bert, XLNet ...):bertabs

Language I am using the model on (English, Chinese ...):English

The problem arises when using:
* [ ] the official example scripts: (give details below) - Yes
* [ ] my own modified scripts: (give details below)

The tasks I am working on is:
* [ ] an official GLUE/SQUaD task: (give the name)
* [ ] my own task or dataset: (give details below) - my own task

