Can't install transformers from sources using poetry
# 🐛 Bug

When installing transformers from sources using poetry

```bash
poetry add git+https://github.com/huggingface/transformers.git
```

The following exception is thrown:

```bash
[InvalidRequirement]
Invalid requirement, parse error at "'extra =='"
```

This is a problem on poetry side. The issue here is just to cross-link the problem.

Ref: https://github.com/python-poetry/poetry/issues/2326


In the meantime as a workaround, you can do the following:

1) Fork huggingface/transformers
2) On your fork remove this line https://github.com/huggingface/transformers/blob/97a375484c618496691982f62518130f294bb9a8/setup.py#L79
3) Install your fork with poetry<|||||>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.
