summary_type value  of SequenceSummary is incorrect
https://github.com/huggingface/transformers/blob/0477b307c7501ea76e01b03cb387a2312db752b3/transformers/modeling_utils.py#L731

I think `if hasattr(config, 'summary_use_proj')` is incorrect, `if hasattr(config, 'summary_type')` is correct.
Thanks!