title: Plots and widgets not showing on jupyter lab
body: <p>If I run this code on a <code>jupyter notebook</code></p>
  
  <pre><code>from bqplot import pyplot as plt
  import numpy as np
  
  plt.figure(1, title='Line Chart')
  np.random.seed(0)
  n = 200
  x = np.linspace(0.0, 10.0, n)
  y = np.cumsum(np.random.randn(n))
  plt.plot(x, y)
  plt.show()
  </code></pre>
  
  <p>The plot display, but if I run the same code on Jupyter lab I get</p>
  
  <pre><code>VBox(children=(Figure(axes=[Axis(scale=LinearScale()), Axis(orientation='vertical', scale=LinearScale())], fig…
  </code></pre>
  
  <p>How do I fix this?</p>