title: Jupyter widget does not appear in notebook
body: <p>I'm running a jupyter notebook but the jupyter widgets does not appear. Instead I receive the folllowing message:</p>
  
  <pre><code>Failed to display Jupyter Widget of type Button.
  If you're reading this message in the Jupyter Notebook or JupyterLab Notebook, it may mean that the widgets JavaScript is still loading. If this message persists, it likely means that the widgets JavaScript library is either not installed or not enabled. See the Jupyter Widgets Documentation for setup instructions.
  If you're reading this message in another frontend (for example, a static rendering on GitHub or NBViewer), it may mean that your frontend doesn't currently support widgets.
  </code></pre>
  
  <p>I have the following versions:</p>
  
  <pre><code>widgetsnbextension (3.0.8)
  ipywidgets (7.0.5)
  </code></pre>
  
  <p>I installed the widgets with this command:</p>
  
  <pre><code>pip install ipywidgets
  jupyter nbextension enable --py widgetsnbextension
  </code></pre>
  
  <p>Also my code is:</p>
  
  <pre><code>import ipywidgets as widgets
  from IPython.display import display
  
  button = widgets.Button(description='Hello')
  display(button)
  </code></pre>