Ignore .mypy_cache

This folder is now generate by the mypy tests.

Change-Id: I90ba009e977df75f53904878ba4715c0be3b499f
diff --git a/.gitignore b/.gitignore
index a2dd0a3..d7e2fac 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,6 +3,7 @@
 *.egg-info
 *.pyc
 .idea
+.mypy_cache
 .test
 .testrepository
 .tox