Fix of first interactivity example in advanced_matplotlib

ipynb/11b_advanced_matplotlib.ipynb

@@ -280,11 +280,11 @@
 
 X = np.arange(0, 10, 0.01)
 l, = plt.plot(X, X**2)
 
 def change_color(event):
-    ax.add.set_color('green')
+    l.set_color('green')
     
 f.canvas.mpl_connect('button_press_event', change_color)
 ```
 
 %% Cell type:markdown id: tags: