Add mypy cache to gitignore (GH-6614)

onlined · brettcannon · commit 5a49ca61d2f0 · 2018-04-30T12:10:45.000-07:00
diff --git a/.gitignore b/.gitignore
@@ -114,3 +114,4 @@ Tools/ssl/win32
 .vs/
 .vscode/
 gmon.out
+.mypy_cache/
