Merge pull request matplotlib#9328 from cgohlke/patch-2

Fix NameError: name 'os' is not defined

Author: dstansby

examples/animation/movie_demo_sgskip.py

@@ -7,6 +7,7 @@
 
 from __future__ import print_function
 
+import os
 import subprocess
 import matplotlib.pyplot as plt
 import numpy as np