title: issue with func in matplotlib.FuncAnimation not updating data
body: <pre><code>fig = plt.figure()
  ax = fig.add_subplot(111, projection='3d')
  ax.set_xlabel('x')
  ax.set_ylabel('y')
  ax.set_zlabel('z')
  ax.set_xlim([0, 1])
  ax.set_ylim([0, 1])
  ax.set_zlim([0, 90]) 
  
  x = np.linspace(xL, xR, nx)
  z = np.linspace(zL, zR, nz)
  X, Z = np.meshgrid(x, z)
  r = T[:,5,:,0]
  
  graph = ax.plot_surface(X, Z, r)
  
  def update_graph(q):
      r = T[:,5,:,q]
      graph.set_3d_properties(r)
      return graph
  
  ani = matplotlib.animation.FuncAnimation(fig, update_graph, frames = 11)
  plt.show()
  </code></pre>
  
  <p>I have the code above, T is a 100x100x100x12 matrix, and I want to make an animation showing a surface plot as the 4th axis goes from 0-11. However it seems that the animation portion is not working  correctly, and I believe the issue is in my update_graph function that it is not passing back an updated value of r to be used in the plot. </p>