Error in run_ner.py
## Environment info

- `transformers` version: 3.0.2
- Platform: Windows-10-10.0.19041-SP0
- Python version: 3.8.3
- PyTorch version (GPU?): 1.6.0 (True)
- Tensorflow version (GPU?): not installed (NA)
- Using GPU in script?: <fill in>
- Using distributed or parallel set-up in script?: <fill in>

### Who can help
 
@stefan-it 

## Information

The problem arises when using:
* [ ] the official example scripts: (give details below)
* [X] my own modified scripts: (give details below)

The tasks I am working on is:
* [X] an official GLUE/SQUaD task: Rare Entities task: WNUT’17 (English NER) dataset
* [ ] my own task or dataset: (give details below)

## To reproduce

Steps to reproduce the behavior:

When I try to execute run_ner.py, the following error occurs:

08/27/2020 16:10:10 - INFO - filelock -   Lock 2174122787120 acquired on ./data_wnut_17\cached_dev_BertTokenizer_128.lock
08/27/2020 16:10:24 - INFO - utils_ner -   Creating features from dataset file at ./data_wnut_17
08/27/2020 16:12:04 - INFO - filelock -   Lock 2174122787120 released on ./data_wnut_17\cached_dev_BertTokenizer_128.lock
Traceback (most recent call last):
  File "C:\Users\Monique\Documents\IA\NLP\transformers\examples\token-classification\utils_ner.py", line 247, in __init__
    examples = token_classification_task.read_examples_from_file(data_dir, mode)
  File "C:\Users\Monique\Documents\IA\NLP\transformers\examples\token-classification\tasks.py", line 27, in read_examples_from_file
    for line in f:
  File "C:\ProgramData\Anaconda3\lib\codecs.py", line 322, in decode
    (result, consumed) = self._buffer_decode(data, self.errors, final)
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xb4 in position 46: invalid start byte

My only local change was the following in preprocess.py:

`with open(dataset, "rt", encoding='utf-8') as f_p:`

(I added encoding='utf-8' due to a similar error in preprocessing).

## Expected behavior

The dataset should have been created without encoding errors.

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.
