Unable to download wikidata

Running `./dataset.py download --dataset wikidata` produces the following error:

```
subprocess.CalledProcessError: Command 'wget -O data/external/wikidata-claims_instance-of.jsonl https://s3-us-west-2.amazonaws.com/pinafore-us-west-2/qanta-jmlr-datasets/wikidata-claims_instance-of.jsonl' returned non-zero exit status 8.
```