Problem re-building JupyterLab on Windows

Hello,

I want to install the Matplotlib extension for JupyterLab but when I install it and run:

 jupyter lab build

I get this error on the npm step:

> jupyter-matplotlib@0.8.2 build:labextension c:\program files\python3\share\jupyter\lab\staging\node_modules\jupyter-matplotlib
> jupyter labextension build .

Please supply at least one subcommand: check, disable, enable, install, link, list, uninstall, unlink, update
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! jupyter-matplotlib@0.8.2 build:labextension: `jupyter labextension build .`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the jupyter-matplotlib@0.8.2 build:labextension script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.