Merge pull request #487 from marshmallow-code/dependabot/pip/mypy-0.770

Bump mypy from 0.761 to 0.770

Author: lafrech

setup.py

@@ -22,7 +22,7 @@
     ]
     + FRAMEWORKS,
     "lint": [
-        "mypy==0.761",
+        "mypy==0.770",
         "flake8==3.7.9",
         "flake8-bugbear==20.1.4",
         "pre-commit>=1.20,<3.0",