[Bug][Jupyter Widget] Plugin 'keplergl-jupyter' failed to activate

**Describe the bug**
JupyterLab browser console reports

"Plugin 'keplergl-jupyter' failed to activate."
"Error: No provider for: jupyter.extensions.jupyterWidgetRegistry."

Trying to instantiate widget gives
"Error displaying widget: model not found" in the notebook
"Error: Module keplergl-jupyter, semver range ^0.3.0 is not registered as a widget module" in the console

**To Reproduce**
1) `conda create -n jupyterlab-kepler python`
2) `pip install jupyterlab keplergl`
3) `conda install nodejs`
4) `jupyter labextension install @jupyter-widgets/jupyterlab-manager keplergl-jupyter`
5) `jupyter lab`
6) Use basic Python code from doc site

**Expected behavior**
Widget appears and is usable

**Environment (please complete the following information):**
Python 3.9.5
keplergl widget version 0,3.0