cannot load data from my loacal path
Hi ! The `data_files` parameter must be a string, a list/tuple or a python dict.

Can you check the type of your `config.train_path` please ? Or use `data_files=str(config.train_path)` ?
## Describe the bug
I just want to directly load data from my local path,but find a bug.And I compare it with pandas to provide my local path is real.

here is my code
```python3
# print my local path
print(config.train_path)
# read data and print data length
tarin=pd.read_csv(config.train_path)
print(len(tarin))

# loading data by load_dataset 
data = load_dataset('csv',data_files=config.train_path)

print(len(data))
```


## Steps to reproduce the bug
```python
C:\Users\wie\Documents\项目\文本分类\data\train.csv
7613
Traceback (most recent call last):
  File "c:/Users/wie/Documents/项目/文本分类/lib/DataPrecess.py", line 17, in <module>
    data = load_dataset('csv',data_files=config.train_path)
  File "C:\Users\wie\Miniconda3\lib\site-packages\datasets\load.py", line 830, in load_dataset
    **config_kwargs,
  File "C:\Users\wie\Miniconda3\lib\site-packages\datasets\load.py", line 710, in load_dataset_builder
    **config_kwargs,
  File "C:\Users\wie\Miniconda3\lib\site-packages\datasets\builder.py", line 271, in __init__
    **config_kwargs,
  File "C:\Users\wie\Miniconda3\lib\site-packages\datasets\builder.py", line 386, in _create_builder_config
    config_kwargs, custom_features=custom_features, use_auth_token=self.use_auth_token
  File "C:\Users\wie\Miniconda3\lib\site-packages\datasets\builder.py", line 156, in create_config_id
    raise ValueError("Please provide a valid `data_files` in `DatasetBuilder`")
ValueError: Please provide a valid `data_files` in `DatasetBuilder`
```

## Expected results
A clear and concise description of the expected results.

## Actual results
Specify the actual results or traceback.

## Environment info
<!-- You can run the command `datasets-cli env` and copy-and-paste its output below. -->
- `datasets` version:  1.11.0
- Platform: win10
- Python version: 3.7.9
- PyArrow version: 5.0.0
