The appveyor build is failing fairly consistently on the python 3.5 build (eg. see https://ci.appveyor.com/project/matplotlib/matplotlib/build/1.0.2957/job/dqhano9lykge7ffb#L1375). The actual failure is somewhere in test_artist:

lib\matplotlib\tests\test_artist.py ...ssCommand exited with code -1073740791