Update marshmallow to 3.12.1

[pyup-bot]

This PR updates marshmallow from 3.10.0 to 3.12.1.

Changelog

3.12.1

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

Bug fixes:

- Fix bug that raised an ``AttributeError`` when instantiating a
``Schema`` with a field named ``parent`` (:issue:`1808`).
Thanks :user:`flying-sheep` for reporting and helping with the fix.

3.12.0

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

Features:

- Add ``validate.And`` (:issue:`1768`).
Thanks :user:`rugleb` for the suggestion.
- Add type annotations to ``marshmallow.decorators`` (:issue:`1788`, :pr:`1789`).
Thanks :user:`michaeldimchuk` for the PR.
- Let ``Field``\s be accessed by name as ``Schema`` attributes (:pr:`1631`).

Other changes:

- Improve types in ``marshmallow.validate`` (:pr:`1786`).
- Make ``marshmallow.validate.Validator`` an abstract base class (:pr:`1786`).
- Remove unnecessary list cast (:pr:`1785`).

3.11.1

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

Bug fixes:

- Fix treatment of dotted keys when ``unknown=INCLUDE`` (:issue:`1506`).
Thanks :user:`rbu` for reporting and thanks :user:`sirosen` for the fix (:pr:`1745`).

3.11.0

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

Features:

- Add ``fields.IPInterface``, ``fields.IPv4Interface``, and
``IPv6Interface`` (:issue:`1733`). Thanks :user:`madeinoz67`
for the suggestion and the PR.
- Raise ``AttributeError`` for missing methods when using ``fields.Method`` (:pr:`1675`).
Thanks :user:`lassandroan`.

Other changes:

- Remove unnecessary ``hasattr`` and ``getattr`` checks in ``Field`` (:pr:`1770`).

Links

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

[coveralls]

Coverage remained the same at 86.667% when pulling 8238826 on pyup-update-marshmallow-3.10.0-to-3.12.1 into e3b6dee on master.

[pyup-bot]

Closing this in favor of #318