title: Pyplot 3D scatter z axis issue
body: <p>Is there something wrong with the 3d plt.scatter(x,y,z) method?</p>
  <p>Plots all z values at zero:</p>
  <pre><code>x = [1, 1]
  y = [1, 1]
  z = [-10, 10]
  
  fig = plt.figure(figsize=(16, 18))
  plt.axes(projection =&quot;3d&quot;)
  plt.scatter(x, y, z, color='k')
  
  plt.show()
  </code></pre>
  <p>Working correctly:</p>
  <pre><code>x = [1, 1]
  y = [1, 1]
  z = [-10, 10]
  
  fig = plt.figure(figsize=(16, 18))
  ax = plt.axes(projection =&quot;3d&quot;)
  ax.scatter(x, y, z, color='k')
  
  plt.show()
  </code></pre>