Bump marshmallow from 2.18.0 to 3.9.1

Bumps marshmallow from 2.18.0 to 3.9.1.

Changelog

Sourced from marshmallow's changelog.

3.9.1 (2020-11-07)

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Bug fixes:

• Cast to mapping type in Mapping.serialize and Mapping.deserialize (🇵🇷1685).
• Fix bug letting Dict pass invalid dict on deserialization when no key or value Field is specified (🇵🇷1685).

3.9.0 (2020-10-31)

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Features:

• Add format argument to fields.Time and timeformat class Meta option (:issue:686). Thanks :user:BennyAlex for the suggestion and thanks :user:infinityxxx for the PR.

Other changes:

• Remove usage of implicit typing.Optional (:issue:1663). Thanks :user:nadega for the PR.

3.8.0 (2020-09-16)

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Features:

• Add fields.IP, fields.IPv4 and fields.IPv6 (🇵🇷1485). Thanks :user:mgetka for the PR.

Bug fixes:

• Fix typing in AwareDateTime (🇵🇷1658). Thanks :user:adithyabsk for reporting.

3.7.1 (2020-07-20)

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Bug fixes:

• fields.Boolean correctly serializes non-hashable types (🇵🇷1633). Thanks :user:jun0jang for the PR.

3.7.0 (2020-07-08)

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Deprecations:

• marshmallow.pprint is deprecated and will be removed in marshmallow 4 (:issue:1588).

... (truncated)

Commits

• d438729 Bump version and update changelog
• ad93940 Merge pull request #1685 from marshmallow-code/dict_cast_mapping_type
• aa27968 Update CHANGELOG
• 8113031 Remove broken "bad dict" tests
• b277354 Mapping field: cast to mapping type
• ef0fc76 Various docs updates (#1687)
• e1cf222 Bump sphinx from 3.2.1 to 3.3.0
• 739ec29 Bump version and update changelog
• c30d3eb Add format option for fields.time #686 (#1682)
• f37da1a Test against Python 3.9 (#1680)
• Additional commits viewable in compare view