Test failure: KeyError: 'textColor'

When trying to run tests locally, I get the following test failure:

```
>       assert marker._folium_kwargs['icon'].options['textColor'], 'gray'
E       KeyError: 'textColor'

tests/test_maps.py:166: KeyError
```

This might be a result of using a newer version of folium on my local machine (folium 0.20.0).