Dancing x-axis in animation [solved]

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I'm very new to sage, and I'm trying to make the following animation:

a = animate([sin(20*(x - float(k)))/x for k in srange(0,2*pi,0.5)], 
           xmin=1, xmax=4, figsize=[3,2])
a.gif(savefile='my_animation.gif', show_path=True)

The problem is that if you look at the animation you'll notice that the x-axis is moving all the time which I find very distracting. Is there a way to tell sage that I want to center the x-axis, so that it stops moving with the animation?