Merge pull request #150 from enter-at/renovate/marshmallow-3.x

chore(deps): update dependency marshmallow to v3.13.0

Author: alexsavio

dev-requirements.txt

@@ -18,4 +18,4 @@ rope
 twine
 pydocstyle
 jsonschema==3.2.0
-marshmallow==3.9.0
+marshmallow==3.13.0