the pile datasets url seems to change back
### Describe the bug

in #3627, the host url of the pile dataset became `https://mystic.the-eye.eu`. Now the new url is broken, but `https://the-eye.eu` seems to work again.

### Steps to reproduce the bug

```python3
from datasets import load_dataset
dataset = load_dataset("bookcorpusopen")
```
shows
```python3
ConnectionError: Couldn't reach https://mystic.the-eye.eu/public/AI/pile_preliminary_components/books1.tar.gz (ProxyError(MaxRetryError("HTTPSConnectionPool(host='mystic.the-eye.eu', port=443): Max retries exceeded with url: /public/AI/pile_pr
eliminary_components/books1.tar.gz (Caused by ProxyError('Cannot connect to proxy.', OSError('Tunnel connection failed: 504 Gateway Timeout')))")))
```

### Expected behavior

Downloading as normal.

### Environment info

- `datasets` version: 2.9.0
- Platform: Linux-5.4.143.bsk.7-amd64-x86_64-with-glibc2.31
- Python version: 3.9.2
- PyArrow version: 6.0.1
- Pandas version: 1.5.3
Thanks for reporting, @wjfwzzc.

I am transferring this issue to the corresponding dataset on the Hub: https://huggingface.co/datasets/bookcorpusopen/discussions/1 Thank you. All fixes are done:
- [x] https://huggingface.co/datasets/bookcorpusopen/discussions/2
- [x] https://huggingface.co/datasets/the_pile/discussions/1
- [x] https://huggingface.co/datasets/the_pile_books3/discussions/1
- [x] https://huggingface.co/datasets/the_pile_openwebtext2/discussions/2
- [x] https://huggingface.co/datasets/the_pile_stack_exchange/discussions/2