Update mypy from 0.711 to 0.720

Release notes: http://mypy-lang.blogspot.com/2019/07/mypy-0720-released.html

Author: bluetech

.pre-commit-config.yaml

@@ -44,7 +44,7 @@ repos:
     hooks:
     -   id: rst-backticks
 -   repo: https://github.com/pre-commit/mirrors-mypy
-    rev: v0.711
+    rev: v0.720
     hooks:
     -   id: mypy
         files: ^(src/|testing/)