importing nvd3 hangs python

This seems to hang. Does anyone else have such issues?


```python
$ cat /tmp/test_import_nvd3.py
print('start')

import nvd3

print('end')
```

```bash
$ python3.8 /tmp/test_import_nvd3.py
start
```

Tested against python 3.8.7 on Debian using `python-nvd3==0.15.0`.