plotly.py: Installing plotly with ipywigets 7.5 fails to plot in jupyter lab

Hi,

I noticed that if I upgrade to the latest version of ipywidgets==7.5 this breaks FigureWidget in my jupyter lab notebook (in offline mode).

The part of my docker file that install plotly looks like this:

RUN pip install plotly==3.10.0 jupyterlab==0.35 ipywidgets==7.5 psutil

# Install Jupyter Lab Extensions
# ------------------------------------------------------------------------------
RUN export NODE_OPTIONS=--max-old-space-size=4096 \
    && jupyter labextension install @jupyter-widgets/jupyterlab-manager@0.38 --no-build \
    && jupyter labextension install plotlywidget@0.11.0 --no-build \
    && jupyter labextension install @jupyterlab/plotly-extension@0.18.2 --no-build \
    && jupyter lab build

I get the “Error displaying widget” message. Looking in the console gives me this error:

Uncaught (in promise) Module @jupyter-widgets/base, semver range ^1.2.0 is not registered as a widget module
vendors~main.dfdb0f7451aa8d94f759.js:460982 Error displaying widget
vendors~main.dfdb0f7451aa8d94f759.js:460983 Module @jupyter-widgets/base, semver range ^1.2.0 is not registered as a widget module

If I revert back to 7.4 then the error goes away. I only noticed this because I originally had my ipywidgets install line set to "ipywidgets>=7.2" which is what the plotly.py install instructions recommend.