title: Jupyter-matplotlib: Error displaying widget: model not found
body: <p>I'm trying to install jupyter-matplotlib extension but can't make it work in a jupyterlab instance.
  Once installed by following the steps here:<br />
  <a href="https://github.com/matplotlib/jupyter-matplotlib" rel="noreferrer">https://github.com/matplotlib/jupyter-matplotlib</a><br />
  I get the error when executing a simple example:<br />
  <em>Error displaying widget: model not found</em><br />
  <img src="https://i.stack.imgur.com/LDEnL.png" alt="screen capture of described behaviour" /></p>
  <p>Here's the output of my <code>$ conda list</code> for relevant packages:</p>
  <p>ipykernel                 5.1.1<br />
  ipympl                    0.2.1<br />
  ipython                   7.6.1<br />
  ipython_genutils          0.2.0<br />
  ipywidgets                7.5.0<br />
  jupyter_client            5.3.1<br />
  jupyter_core              4.4.0<br />
  jupyterlab                1.0.2<br />
  jupyterlab_server         1.0.0</p>