UnicodeDecodeError when downloading GLUE-MNLI
It should be good now, thanks for noticing and fixing it ! I would say that it was because you are on windows but not 100% sure
When I run
```python
dataset = nlp.load_dataset('glue', 'mnli')
```
I get an encoding error (could it be because I'm using Windows?) :
```python
# Lots of error log lines later...
~\Miniconda3\envs\nlp\lib\site-packages\tqdm\std.py in __iter__(self)
   1128         try:
-> 1129             for obj in iterable:
   1130                 yield obj

~\Miniconda3\envs\nlp\lib\site-packages\nlp\datasets\glue\5256cc2368cf84497abef1f1a5f66648522d5854b225162148cb8fc78a5a91cc\glue.py in _generate_examples(self, data_file, split, mrpc_files)
    529 
--> 530                 for n, row in enumerate(reader):
    531                     if is_cola_non_test:

~\Miniconda3\envs\nlp\lib\csv.py in __next__(self)
    110             self.fieldnames
--> 111         row = next(self.reader)
    112         self.line_num = self.reader.line_num

~\Miniconda3\envs\nlp\lib\encodings\cp1252.py in decode(self, input, final)
     22     def decode(self, input, final=False):
---> 23         return codecs.charmap_decode(input,self.errors,decoding_table)[0]
     24 

UnicodeDecodeError: 'charmap' codec can't decode byte 0x9d in position 6744: character maps to <undefined>
```
Anyway this can be solved by specifying to decode in UTF when reading the csv file. I am proposing a PR if that's okay.
UnicodeDecodeError when downloading GLUE-MNLI 
 When I run
```python
dataset = nlp.load_dataset('glue', 'mnli')
```
I get an encoding error (could it be because I'm using Windows?) :
```python
# Lots of error log lines later...
~\Miniconda3\envs\nlp\lib\site-packages\tqdm\std.py in __iter__(self)
   1128         try:
-> 1129             for obj in iterable:
   1130                 yield obj

~\Miniconda3\envs\nlp\lib\site-packages\nlp\datasets\glue\5256cc2368cf84497abef1f1a5f66648522d5854b225162148cb8fc78a5a91cc\glue.py in _generate_examples(self, data_file, split, mrpc_files)
    529 
--> 530                 for n, row in enumerate(reader):
    531                     if is_cola_non_test:

~\Miniconda3\envs\nlp\lib\csv.py in __next__(self)
    110             self.fieldnames
--> 111         row = next(self.reader)
    112         self.line_num = self.reader.line_num

~\Miniconda3\envs\nlp\lib\encodings\cp1252.py in decode(self, input, final)
     22     def decode(self, input, final=False):
---> 23         return codecs.charmap_decode(input,self.errors,decoding_table)[0]
     24 

UnicodeDecodeError: 'charmap' codec can't decode byte 0x9d in position 6744: character maps to <undefined>
```
Anyway this can be solved by specifying to decode in UTF when reading the csv file. I am proposing a PR if that's okay. 
 It should be good now, thanks for noticing and fixing it ! I would say that it was because you are on windows but not 100% sure