title: Lines missing in 3d scatterplot
body: <p>I can't find the reason why my plot shows no lines....</p>
  <pre><code>fig = plt.figure()
  ax = fig.gca(projection='3d')
  for i in range(n):
      ax.scatter(lys[i][0], lys[i][1], lys[i][2], c='b', marker='o')
  ax.plot(x, y, z,'bo', label='Self-avoiding random walk')
  ax.legend()
  plt.show()
  </code></pre>