DOC: use figure.canvas.draw_idle rather than plt.draw

Local is better than global

Author: tacaswell

examples/widgets/check_buttons.py

@@ -39,7 +39,7 @@
 def callback(label):
     ln = lines_by_label[label]
     ln.set_visible(not ln.get_visible())
-    plt.draw()
+    ln.figure.canvas.draw_idle()
 
 check.on_clicked(callback)