title: plot.ly offline mode in jupyter lab not displaying plots
body: <p>According to the documentation, <a href="https://plot.ly/python/offline/" rel="noreferrer">offline mode with plot.ly</a> in Jupyter is supposed to work after calling:</p>
  
  <pre><code>from plotly.offline import download_plotlyjs, init_notebook_mode, iplot
  init_notebook_mode(connected=True)
  </code></pre>
  
  <p>Now I am trying to show the following plot:</p>
  
  <pre><code>trace0 = plotly.graph_objs.Scatter(
      x=[1, 2, 3, 4],
      y=[10, 15, 13, 17]
  )
  trace1 = plotly.graph_objs.Scatter(
      x=[1, 2, 3, 4],
      y=[16, 5, 11, 9]
  )
  
  iplot([trace0, trace1])
  </code></pre>
  
  <p>The result is much empty space in the cell output area.</p>
  
  <p><a href="https://i.stack.imgur.com/4ghrI.png" rel="noreferrer"><img src="https://i.stack.imgur.com/4ghrI.png" alt="enter image description here"></a></p>
  
  <p>Why is this not working with Jupyter Lab?</p>