Remove deprecated field usage

The 'default' argument to fields is deprecated in Marshmallow. Use 'dump_default' instead.

Solves lidatong#546

Author: rianwouters

dataclasses_json/mm.py

@@ -305,7 +305,7 @@ def schema(cls, mixin, infer_missing):
         else:
             type_ = field.type
             options: typing.Dict[str, typing.Any] = {}
-            missing_key = 'missing' if infer_missing else 'default'
+            missing_key = 'missing' if infer_missing else 'dump_default'
             if field.default is not MISSING:
                 options[missing_key] = field.default
             elif field.default_factory is not MISSING: