bookcorpusopen no longer works
Hi ! Thanks for reporting :) I think #3280 should fix this I tried with the latest changes from #3280 on google colab and it worked fine :)
We'll do a new release soon, in the meantime you can use the updated version with:
```python
load_dataset("bookcorpusopen", revision="master")
``` Fixed by #3280.
## Describe the bug

When using the latest version of datasets (1.14.0), I cannot use the `bookcorpusopen` dataset. The process blocks always around `9924 examples [00:06, 1439.61 examples/s]` when preparing the dataset. I also noticed that after half an hour the process is automatically killed because of the RAM usage (the machine has 1TB of RAM...).

This did not happen with 1.4.1.
I tried also `rm -rf ~/.cache/huggingface` but did not help.
Changing python version between 3.7, 3.8 and 3.9 did not help too.

## Steps to reproduce the bug
```python
import datasets
d = datasets.load_dataset('bookcorpusopen')
```

## 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: 1.14.0
- Platform: Linux-5.4.0-1054-aws-x86_64-with-glibc2.27
- Python version: 3.9.7
- PyArrow version: 4.0.1
