`pubmed_qa` checksum mismatch
## Describe the bug
Loading [`pubmed_qa`](https://huggingface.co/datasets/pubmed_qa) results in a mismatched checksum error.

## Steps to reproduce the bug
```python
# Sample code to reproduce the bug
import datasets
try:
    datasets.load_dataset("pubmed_qa", "pqa_labeled")
except Exception as e:
    print(e)

try:
    datasets.load_dataset("pubmed_qa", "pqa_unlabeled")
except Exception as e:
    print(e)

try:
    datasets.load_dataset("pubmed_qa", "pqa_artificial")
except Exception as e:
    print(e)
```

## Expected results
Successful download.

## Actual results
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.9/site-packages/datasets/load.py", line 1702, in load_dataset
    builder_instance.download_and_prepare(
  File "/usr/local/lib/python3.9/site-packages/datasets/builder.py", line 594, in download_and_prepare
    self._download_and_prepare(
  File "/usr/local/lib/python3.9/site-packages/datasets/builder.py", line 665, in _download_and_prepare
    verify_checksums(
  File "/usr/local/lib/python3.9/site-packages/datasets/utils/info_utils.py", line 40, in verify_checksums
    raise NonMatchingChecksumError(error_msg + str(bad_urls))
datasets.utils.info_utils.NonMatchingChecksumError: Checksums didn't match for dataset source files:
['https://drive.google.com/uc?export=download&id=1RsGLINVce-0GsDkCLDuLZmoLuzfmoCuQ', 'https://drive.google.com/uc?export=download&id=15v1x6aQDlZymaHGP7cZJZZYFfeJt2NdS']

## Environment info
<!-- You can run the command `datasets-cli env` and copy-and-paste its output below. -->
- `datasets` version: 1.18.3
- Platform: macOS
- Python version: 3.8.1
- PyArrow version: 3.0.0
