Update marshmallow to 3.3.0

[pyup-bot]

This PR updates marshmallow from 3.2.1 to 3.3.0.

Changelog

3.3.0

******************

Features:

- ``fields.Nested`` may take a callable that returns a schema instance.
Use this to resolve order-of-declaration issues when schemas nest each other (:issue:`1146`).

.. code-block:: python

  <3.3
 class AlbumSchema(Schema):
     title = fields.Str()
     artist = fields.Nested("ArtistSchema", only=("name",))


 class ArtistSchema(Schema):
     name = fields.Str()
     albums = fields.List(fields.Nested(AlbumSchema))


  >=3.3
 class AlbumSchema(Schema):
     title = fields.Str()
     artist = fields.Nested(lambda: ArtistSchema(only=("name",)))


 class ArtistSchema(Schema):
     name = fields.Str()
     albums = fields.List(fields.Nested(AlbumSchema))

Deprecations:

- Passing the string ``"self"`` to ``fields.Nested`` is deprecated.
Use a callable instead.

.. code-block:: python

 from marshmallow import Schema, fields

  <3.3
 class PersonSchema(Schema):
     partner = fields.Nested("self", exclude=("partner",))
     friends = fields.List(fields.Nested("self"))


  >=3.3
 class PersonSchema(Schema):
     partner = fields.Nested(lambda: PersonSchema(exclude=("partner")))
     friends = fields.List(fields.Nested(lambda: PersonSchema()))

Other changes:

- Fix typing for ``Number._format_num`` (:pr:`1466`). Thanks :user:`hukkinj1`.
- Make mypy stricter and remove dead code (:pr:`1467`). Thanks again, :user:`hukkinj1`.

3.2.2

******************

Bug fixes:

- Don't load fields for which ``load_only`` and ``dump_only`` are both ``True`` (:pr:`1448`).
- Fix types in ``marshmallow.validate`` (:pr:`1446`).

Support:

- Test against Python 3.8 (:pr:`1431`).

Links

• PyPI: https://pypi.org/project/marshmallow
• Changelog: https://pyup.io/changelogs/marshmallow/
• Repo: https://github.com/marshmallow-code/marshmallow

[pyup-bot]

Closing this in favor of #206