Fix pytorch lighting examples
It throws the exception 'Trainer' object has no attribute 'avg_loss' because since version 0.7.2 they removed the avg_loss field from the Trainer class.

Also `get_tqdm_dict` is deprecated since 0.7.3.

See https://github.com/huggingface/transformers/pull/2890#issuecomment-613066707
@simonepri can you point to the examples that need fixing?<|||||>https://github.com/huggingface/transformers/blob/master/examples/glue/run_pl_glue.py
https://github.com/huggingface/transformers/blob/master/examples/ner/run_pl_ner.py
<|||||>This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
