reddit_tifu dataset: Checksums didn't match for dataset source files
Hi @XingxingZhang, 

We have already fixed this. You should update `datasets` version to at least 1.18.4:
```shell
pip install -U datasets
```
And then force the redownload:
```python
load_dataset("...", download_mode="force_redownload")
```

Duplicate of:
- #3773 thanks @albertvillanova . by upgrading to 1.18.4 and using `load_dataset("...", download_mode="force_redownload")` fixed 
 the bug.

using the following as you suggested in another thread can also fixed the bug
```
pip install git+https://github.com/huggingface/datasets#egg=datasets
```
 The latter solution (installing from GitHub) was proposed because the fix was not released yet. But last week we made the 1.18.4 patch release (with the fix), so no longer necessary to install from GitHub.

You can now install from PyPI, as usual:
```shell
pip install -U datasets
```

## Describe the bug
When loading the reddit_tifu dataset, it throws the exception "Checksums didn't match for dataset source files"


## Steps to reproduce the bug
```python
import datasets
from datasets import load_dataset

print(datasets.__version__)

# load_dataset('billsum')

load_dataset('reddit_tifu', 'short')
```


## Environment info
<!-- You can run the command `datasets-cli env` and copy-and-paste its output below. -->
- `datasets` version: 1.17.0
- Platform: mac os
- Python version: Python 3.7.6
- PyArrow version: 3.0.0
