Extension Enable issue during sankey install

[jgiegel]

@ricklupton any insight? Seem to have any issue with the extension for the sankey widget. Tried the standard install protocols, multiple times.

$ jupyter nbextension list Known nbextensions: config dir: /Users/-/opt/anaconda3/etc/jupyter/nbconfig notebook section ipysankeywidget/extension enabled

• Validating: problems found:
  • require? X ipysankeywidget/extension jupyterlab-plotly/extension enabled
• Validating: OK jupyter-js-widgets/extension enabled
• Validating: OK jupyter-sankey-widget/extension enabled
• Validating: OK

[ricklupton]

Thanks for reporting. I've updated the widget structure in #84 and I think this should be fixed.