title: Ipython interact function plots multiple plots instead of editing the one
body: <p>I am using jupyter v1.00,Ipython v6.0 and conda v4.3.16 for creating interactive plots. I'm using the following code which is supposed to create one plot and editing it after the change, but it creates multiple plots every time the <em>power</em> variable is changed. why it behaves like this? is it a new thing in Ipython 6.0? I can confirm that it is working in Ipython v5.0</p>
  
  <pre><code>%matplotlib inline
  from ipywidgets import interact, IntSlider
  import matplotlib.pylab as plt
  import numpy as np
  
  power_slider = IntSlider(min=1, max=5)
  @interact(power=power_slider)
  def plot(power):
      plt.figure(figsize=(10, 8))
      plt.plot(np.power(range(10), power))
      return plt
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/Z1AnW.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Z1AnW.png" alt="enter image description here"></a></p>