Add mypy

Author: jonodrew

.pre-commit-config.yaml

@@ -20,3 +20,8 @@ repos:
     hooks:
     -   id: flake8
         args: [--max-line-length=131, --extend-ignore=E203]
+
+-   repo: https://github.com/pre-commit/mirrors-mypy
+    rev: v0.971
+    hooks:
+    -   id: mypy