added test_animation to default_test_modules so the tests run

Author: tacaswell

lib/matplotlib/__init__.py

@@ -1292,6 +1292,7 @@ def tk_window_focus():
 
 default_test_modules = [
     'matplotlib.tests.test_agg',
+    'matplotlib.tests.test_animation',
     'matplotlib.tests.test_arrow_patches',
     'matplotlib.tests.test_artist',
     'matplotlib.tests.test_axes',