Bump marshmallow from 2.18.0 to 3.8.0

Bumps marshmallow from 2.18.0 to 3.8.0.

Changelog

Sourced from marshmallow's changelog.

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).

Support:

• Document default_error_messages on field classes (🇵🇷1619). Thanks :user:weeix.

Bug fixes:

• Fix passing only and exclude to Nested with an ordered Schema (🇵🇷1627). Thanks :user:juannorris for the PR.

3.6.1 (2020-06-02)

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No code changes--only docs and contributor-facing updates in this release.

Support:

• Documentation: improve custom fields example (:issue:1538). Thanks :user:pablospizzamiglio for reporting the problem with the old example and thanks :user:Resinderate for the PR.
• Documentation: Split up API reference into multiple pages and add summary tables (🇵🇷1587). Thanks :user:EpicWink for the PR.

... (truncated)

Commits

• a207173 Bump version and update changelog
• a857318 Merge pull request #1485 from mgetka/ip-address-field
• 1a7d92d Merge branch 'dev' into ip-address-field
• 2708795 Merge pull request #1662 from ebargtuo/patch-1
• 4d9b364 Update AUTHORS
• 1bca177 Update CHANGELOG
• fdb36a5 Merge pull request #1658 from marshmallow-code/fix_tz_typing
• 0a3d92c Run black
• f81bc34 Fix path to run the ToDo API app in examples doc
• 707c057 Merge branch '2.x-line' into dev
• Additional commits viewable in compare view