title: Interactive plot with ipyvidgets and matplotlib on binder produces static images
body: <p>I'm trying to share a github repo on <a href="https://mybinder.org/" rel="nofollow noreferrer">binder</a>. Locally, my interactive plot using matplotlib and @interact works ok. On binder it works half way. Same code adds static images to the cell output in binder notebook when slider value changes.</p>
  <p>Question: how to fix binder behavior and make an interactive plot?</p>
  <p>git repository <a href="https://github.com/queezz/Complex_Numbers" rel="nofollow noreferrer">https://github.com/queezz/Complex_Numbers</a></p>
  <p>My notebook looks like this:</p>
  <pre class="lang-py prettyprint-override"><code>%pylab inline
  </code></pre>
  <pre class="lang-py prettyprint-override"><code>from ipywidgets import interact, widgets
  </code></pre>
  <pre class="lang-py prettyprint-override"><code>x = np.linspace(0,np.pi,100)
  @interact
  def plot_interactive(a=widgets.FloatSlider(min=1, max=10, val=1)):
      plot(x,np.sin(x*a))
      gca().set_aspect('equal')
      ylim(-1.1,1.1)
  </code></pre>
  <p>Screenshot from binder:
  <a href="https://i.stack.imgur.com/wRVWR.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/wRVWR.png" alt="enter image description here" /></a></p>