Run_qa  crashes because of parser = HfArgumentParser((ModelArguments, DataTrainingArguments, TrainingArguments))  
Author: spacemanidol
Pull request: no

## Environment info
- `transformers` version: 4.3.3
- Platform: linux
- Python version:3.7, 3.8, 3.9 reproed across all three
- PyTorch version (GPU?): 1.7, tried 1.8 with same behavior
- Tensorflow version (GPU?):N/A
- Using GPU in script?: yes
- Using distributed or parallel set-up in script?: Yes 2 gpu

### Who can help
@sgugger, @patil-suraj
## Information

Model I am using (Bert, XLNet ...): bert-base-uncased

The problem arises when using:
* [ X] the official example scripts: (give details below)
* [ ] my own modified scripts: (give details below)

The tasks I am working on is:
* [ X] an official GLUE/SQUaD task: (give the name)
* [ ] my own task or dataset: (give details below)
SQUAD 1.0
## To reproduce

Steps to reproduce the behavior:

1. Install clean transformers environment
2. run the run_qa.py script with instructions as specified
3. crash
If you go ahead and create a new environment and install the most recent version of the transformer and try to run the run_qa.py script(SQUAD) it crashes because of a parser issue.


python run_qa.py   --model_name_or_path bert-base-uncased  --dataset_name squad  --do_train  --per_device_train_batch_size 8  --learning_rate 3e-5  --max_seq_length 384  --doc_stride 128  --output_dir output  --overwrite_output_dir  --cache_dir cache  --preprocessing_num_workers 4  --seed 42  --num_train_epochs 1
Traceback (most recent call last):
  File "run_qa.py", line 1095, in <module>
    main()
  File "run_qa.py", line 902, in main
    parser = HfArgumentParser((ModelArguments, DataTrainingArguments, TrainingArguments))
  File "/home/spacemanidol/miniconda3/envs/sparseml/lib/python3.7/site-packages/transformers/hf_argparser.py", line 52, in __init__
    self._add_dataclass_arguments(dtype)
  File "/home/spacemanidol/miniconda3/envs/sparseml/lib/python3.7/site-packages/transformers/hf_argparser.py", line 93, in _add_dataclass_arguments
    elif hasattr(field.type, "__origin__") and issubclass(field.type.__origin__, List):
  File "/home/spacemanidol/miniconda3/envs/sparseml/lib/python3.7/typing.py", line 721, in __subclasscheck__
    return issubclass(cls, self.__origin__)
TypeError: issubclass() arg 1 must be a clas 
## Expected behavior

<!-- A clear and concise description of what you would expect to happen. -->
Run and produce a BERT-QA model

Comments:
This is weird and linked to your environment somehow. 
@stas00 Was this the error you encountered when `dataclasses` is installed in Python 3.7 or was it a different one?

no, that was not that error. I tested `run_qa.py` w/ dataclasses on py38 and it didn't fail.

the datasets error was: `AttributeError: module 'typing' has no attribute '_ClassVar'`

https://github.com/huggingface/transformers/issues/8638

I just tried this on 2 new servers with a fresh conda environment and reproduced behavior. 
Steps.
```bash
conda create -n test python=3.8
conda activate test
pip install transformers datasets torch
python run_qa.py   --model_name_or_path bert-base-uncased  --dataset_name squad  --do_train  --per_device_train_batch_size 8  --learning_rate 3e-5  --max_seq_length 384  --doc_stride 128  --output_dir bert-base-uncased-qa/  --overwrite_output_dir  --cache_dir cache  --preprocessing_num_workers 4  --seed 42  --num_train_epochs 1
```


I have also reproed with venv and regular environment on multiple machines

The suggested commands work fine on my side, so can't reproduce the issue. 

I have pushed a fix (on master by mistake but it's pretty harmless) a tentative fix to remove the line that caused you problem and replace it by a regex. Let me know if it fixes your issue or not (I can't confirm myself since I can't reproduce).

FWIW, I followed your new conda env steps and couldn't reproduce the problem.

@spacemanidol, fyi I edited your comment to fix the conda create line as it had the commands reversed.

Can confirm this works.