title: Matplotlib scatter marker size
body: <p>I'm trying to plot a 3D scatter with <code>matplotlib</code>
  The problem is that I can't change the marker's size
  I have this</p>
  
  <pre><code>scat = plt.scatter([boid_.pos[0] for boid_ in flock],
                     [boid_.pos[1] for boid_ in flock],
                     [boid_.pos[2] for boid_ in flock], 
                     marker='o', s=5)
  </code></pre>
  
  <p>But I get the error</p>
  
  <pre><code>TypeError: scatter() got multiple values for keyword argument 's'
  </code></pre>
  
  <p>Without that, the plot works fine. Where is the problem? Or is there another way to change the size?</p>