Wrong number of examples when loading a text dataset
Hi @kg-nlp, thanks for reporting.

That is weird... I guess we would need some sample data file where this behavior appears to reproduce the bug for further investigation...  ok, I found the reason why that two results are not same.
there is /u2029 in the text, the datasets will split sentence according to the /u2029,but when I use open function will not do that .
so I want to know which function shell do that
thanks
## Describe the bug
when I use load_dataset to read a txt file  I find  that the number of the samples is incorrect

## Steps to reproduce the bug
```
fr = open('train.txt','r',encoding='utf-8').readlines()
print(len(fr))  # 1199637

datasets = load_dataset('text', data_files={'train': ['train.txt']}, streaming=False)
print(len(datasets['train']))  # 1199649
```
I also use command line operation to verify it
```
$ wc -l train.txt 
1199637 train.txt
```

## Expected results
please fix that issue 


## Environment info
<!-- You can run the command `datasets-cli env` and copy-and-paste its output below. -->
- `datasets` version: 1.8.3
- Platform:windows&linux
- Python version:3.7
- PyArrow version:6.0.1
