rerun notebook 02-transformers
Just a notebook rerun (some cells were not executed in the original one).
Few minor changes:
- removed installation cell output for readability (it can't be collapsed in GitHub notebook viewer) 
- added prints with tensors details in the last cell (DE BERT model)

I'm unable to attach nbdiff as html (due to github limitations), hence adding both as zipped 
[nbdiff_02-transformers.zip](https://github.com/huggingface/transformers/files/4623078/nbdiff_02-transformers.zip) and the link to [Gdrive](https://drive.google.com/open?id=1VlucbmczZjUOI8nuCJCAxFoKgjFsJKw0) for your convenience.

Thanks @nikitajz, 

LGTM ! 👍 