Bump marshmallow from 2.18.1 to 3.4.0

[dependabot-preview]

Bumps marshmallow from 2.18.1 to 3.4.0.

Changelog

Sourced from marshmallow's changelog.

3.4.0 (2020-02-02)

Features:

• Improve type coverage (1479). Thanks Reskov.

Bug fixes:

• Fix typing for data param of Schema.load and ValidationError (1492). Thanks mehdigmira for reporting and thanks dfirst for the PR.

Other changes:

• Remove unnecessary typecasts (1500). Thanks hukkinj1.
• Remove useless _serialize override in UUID field (1489).

3.3.0 (2019-12-05)

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 (1146).

# <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.

... (truncated)

Commits

• 64bdd5a Bump version and update changelog
• bad5f33 Don't build other formats
• 358b8f8 Update CHANGELOG and AUTHORS
• 5ffaa19 FIX: fix schema.load(data) typing for many=True case (#1488)
• 8838379 Remove unnecessary typecasts (#1500)
• 709fcbc Merge pull request #1494 from marshmallow-code/dependabot/pip/pre-commit-gte-...
• 294af24 Update pre-commit requirement from ~=1.20 to >=1.20,<3.0
• ff6ad0c Bump flake8-bugbear from 20.1.2 to 20.1.3
• 0855197 Merge pull request #1489 from marshmallow-code/rm_uuid_serialize
• cad9c8f Update CHANGELOG
• Additional commits viewable in compare view

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[dependabot-preview]

Superseded by #106.