BERTScore Error
Hi,

The `use_fast_tokenizer` argument has been recently added to the bert-score lib. I've opened a PR with the fix. In the meantime, you can try to downgrade the version of bert-score with the following command to make the code work:
```
pip uninstall bert-score
pip install "bert-score<0.3.10"
```
## Describe the bug
A clear and concise description of what the bug is.

## Steps to reproduce the bug
```python
predictions = ["hello there", "general kenobi"]
references = ["hello there", "general kenobi"]
bert = load_metric('bertscore')
bert.compute(predictions=predictions, references=references,lang='en')
```

# Bug
`TypeError: get_hash() missing 1 required positional argument: 'use_fast_tokenizer'`


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