[FIX] not training when epoch is small
Closes https://github.com/huggingface/transformers/issues/2995

Solving bug where for small epochs and large gradient_accumulation_steps we never train.
Explained further here: https://github.com/huggingface/transformers/issues/2995
Cool, thanks @mataney! Do you mind running `make style` at the root of the repository to reformat the file according to `black` and `isort`, as indicated in our [contributing guidelines](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md#start-contributing-pull-requests)?

This is so the `check_code_quality` passes.<|||||>@LysandreJik Thanks for your reply.

Recommited with the black formatting.
It is now failing because something else. Do you think you can rerun the tests? I believe it has something to do with the Indeterminism of the tests.

<|||||>Can I have your help here @LysandreJik 