Import time module so that pyplot.pause works

At the moment, there is a bug (GH matplotlib#9412) during the last frame in pyplot interactive mode.
pause() uses time.sleep, but doesn't import the time module.

Author: fikisipi

lib/matplotlib/pyplot.py

@@ -22,6 +22,7 @@
 
 import sys
 import warnings
+import time
 import types
 
 from cycler import cycler