[Bug] Unable to Export Image for Custom MapBox Style

**Describe the bug**
When trying to export an image with a custom MapBox style from kepler.gl the image is empty.

When looking in the network console can see that 3 mapbox API calls have failed with 404s when trying to generate the image

https://api.mapbox.com/v4/mapbox.mapbox-streets-v8,.ckllbil2r320z28lgxyohal18-0bflg,mapbox.mapbox-terrain-v2.json?pluginName=Keplergl&secure&access_token=

https://api.mapbox.com/styles/v1///draft/sprite.json?pluginName=Keplergl&access_token=

https://api.mapbox.com/styles/v1///draft/sprite.png?pluginName=Keplergl&access_token=

**To Reproduce**
Steps to reproduce the behavior:
1. Create a new mapbox style
2. Add a layer of dots based on a tileset of locations
3. Import style into kepler.gl
4. Attempt to export image

**Expected behavior**
Export image exported to be representative of the map, not a blank image.

**Screenshots**



**Desktop:**
- OS: MacOS Big Sur
- Browser: Chrome
- Version: Version 88.0.4324.182 (Official Build) (x86_64)

**Additional context**
Add any other context about the problem here.

Reproduce the export using a custom Mapbox style and inspect the three failed Mapbox API requests described in the issue, including the style sprite and tileset URLs. Trace the image-export path from the request failures; done means the exported image represents the map instead of being blank.

Written by the indexing model from the issue text.