Can't install transformers in Conda environment with python 3.9
## Environment info

- `transformers` version: 4.8.1
- Platform: macOS 11.5.2
- Python version: 3.9.6
- Conda Version: 4.10.3

## Information

I'm trying to install transformers in a condo environment and get and error "conda.exceptions.UnsatisfiableError: The following specifications were found to be incompatible with each other:" with blank lines beneath

## To reproduce

Steps to reproduce the behavior:
``` shell
conda create -n py39 python=3.9
conda activate py39
conda install -c huggingface transformers
```

Verbose conda output of last command:

```
Collecting package metadata (current_repodata.json): ...working... Unable to retrieve repodata (response: 404) for https://conda.anaconda.org/HuggingFace/osx-64/current_repodata.json

done
Solving environment: ...working... failed with initial frozen solve. Retrying with flexible solve.
Solving environment: ...working... failed with repodata from current_repodata.json, will retry with next repodata source.
Collecting package metadata (repodata.json): ...working... done
Solving environment: ...working... failed with initial frozen solve. Retrying with flexible solve.
Solving environment: ...working... 
Found conflicts! Looking for incompatible packages.
This can take several minutes.  Press CTRL-C to abort.
failed                                                                                                                                                                                                                                  
Traceback (most recent call last):
  File "/usr/local/anaconda3/lib/python3.8/site-packages/conda/cli/install.py", line 261, in install
    unlink_link_transaction = solver.solve_for_transaction(
  File "/usr/local/anaconda3/lib/python3.8/site-packages/conda/core/solve.py", line 114, in solve_for_transaction
    unlink_precs, link_precs = self.solve_for_diff(update_modifier, deps_modifier,
  File "/usr/local/anaconda3/lib/python3.8/site-packages/conda/core/solve.py", line 157, in solve_for_diff
    final_precs = self.solve_final_state(update_modifier, deps_modifier, prune, ignore_pinned,
  File "/usr/local/anaconda3/lib/python3.8/site-packages/conda/core/solve.py", line 275, in solve_final_state
    ssc = self._add_specs(ssc)
  File "/usr/local/anaconda3/lib/python3.8/site-packages/conda/core/solve.py", line 706, in _add_specs
    raise UnsatisfiableError({})
conda.exceptions.UnsatisfiableError: 
Did not find conflicting dependencies. If you would like to know which
packages conflict ensure that you have enabled unsatisfiable hints.

conda config --set unsatisfiable_hints True
            

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/anaconda3/lib/python3.8/site-packages/conda/exceptions.py", line 1079, in __call__
    return func(*args, **kwargs)
  File "/usr/local/anaconda3/lib/python3.8/site-packages/conda/cli/main.py", line 84, in _main
    exit_code = do_call(args, p)
  File "/usr/local/anaconda3/lib/python3.8/site-packages/conda/cli/conda_argparse.py", line 83, in do_call
    return getattr(module, func_name)(args, parser)
  File "/usr/local/anaconda3/lib/python3.8/site-packages/conda/cli/main_install.py", line 20, in execute
    install(args, parser, 'install')
  File "/usr/local/anaconda3/lib/python3.8/site-packages/conda/cli/install.py", line 308, in install
    raise e
  File "/usr/local/anaconda3/lib/python3.8/site-packages/conda/cli/install.py", line 295, in install
    unlink_link_transaction = solver.solve_for_transaction(
  File "/usr/local/anaconda3/lib/python3.8/site-packages/conda/core/solve.py", line 114, in solve_for_transaction
    unlink_precs, link_precs = self.solve_for_diff(update_modifier, deps_modifier,
  File "/usr/local/anaconda3/lib/python3.8/site-packages/conda/core/solve.py", line 157, in solve_for_diff
    final_precs = self.solve_final_state(update_modifier, deps_modifier, prune, ignore_pinned,
  File "/usr/local/anaconda3/lib/python3.8/site-packages/conda/core/solve.py", line 275, in solve_final_state
    ssc = self._add_specs(ssc)
  File "/usr/local/anaconda3/lib/python3.8/site-packages/conda/core/solve.py", line 704, in _add_specs
    ssc.r.find_conflicts(spec_set)
  File "/usr/local/anaconda3/lib/python3.8/site-packages/conda/resolve.py", line 352, in find_conflicts
    raise UnsatisfiableError(bad_deps, strict=strict_channel_priority)
conda.exceptions.UnsatisfiableError: The following specifications were found to be incompatible with each other:

Output in format: Requested package -> Available versions

```

## Expected behavior

Installs without error

It seems that its works with python 3.8. Still, I don't get why it wouldn't with 3.9<|||||>Hello! Could you add the unsatisfiable hints with `conda config --set unsatisfiable_hints True` so that we may see what packages are incompatible in python 3.9? Thank you!<|||||>Set the config, nothing has changed<|||||>No this won't change anything, this is so that we may understand what's happening. Please set the config and copy the logs here so that we may help, thank you.<|||||>I know, I meant that the logs stayed absolutely the same. Weird 🤨<|||||>I am having the same issue

```bash
$ conda install -c huggingface transformers
Solving environment: failed

UnsatisfiableError: The following specifications were found to be in conflict:
  - python=3.9
  - transformers
Use "conda info <package>" to see the dependencies for each package.
```

This is a fresh anaconda environment. I did install PyTorch 1.9 with conda, which installs python 3.9.<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md) are likely to be ignored.<|||||>Unstale, this is an actual issue<|||||>I'm able to install latest transformers from the huggingface channel with Python 3.9.7.<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md) are likely to be ignored.