Update rvk requirement from 0.15 to 0.19

[dependabot-preview[bot]]

Updates the requirements on rvk to permit the latest version.

Changelog

Sourced from rvk's changelog.

[0.19.0] - 2020-12-21

Changed

• Type of groups_can_post field in objects::post::Comments has been changed based on API usage and documentation.

[0.18.0] - 2020-07-30

Changed

• The preview field in objects::document::Document has been made optional based on API usage.

[0.17.0] - 2020-05-24

Changed

• Some fields in objects::video::Video have been made optional based on API usage.

[0.16.0] - 2020-05-21

Added

• Undocumented "podcast" attachment type.

Changed

• async/.await support has arrived! :tada:
• Methods now return the type you specify instead of serde_json::Value.
• Switched from failure to thiserror for rvk::Error impl.
• Upgraded reqwest to 0.10.

Removed

• Synchronous access has been removed in favor of async/.await.

[0.15.0] - 2020-03-27

Changed

• Type changes based on actual API behavior (for more details see related commits).

[0.14.0] - 2020-01-26

Changed

• Updated to API version 5.103.

[0.13.0] - 2019-07-04

Changed

• Updated to API version 5.101.

[0.12.0] - 2019-05-11

Changed

• APIClient::new now accepts token: impl Into<String> instead of token: String.
• Updated to API version 5.95.

[0.11.0] - 2019-02-21

Changed

• Added extra field to APIError (#4).
• impl From<&str> instead of impl From<&'static str> for APIError.
• Some tweaks to docs.

Added

• New methods. See 9ca852c.

Commits

• 0721647 Bump version to 0.19.0.
• 72324ad Merge pull request #18 from Iaiao/patch-1
• a8e4961 Change Comments.groups_can_posts to Option<Integer>
• 22128fe Make groups_can_post optional
• 5a55a7e Merge pull request #16 from u32i64/simplify-gh-actions
• e5aac5d Simplify GitHub Actions configuration.
• 2e2f477 Bump version to 0.18.0.
• a8c5f96 Clean up generic method documentation.
• b4377ae Merge pull request #14 from humb1t/patch-2
• 06a9762 Update document object - make preview optional.
• Additional commits viewable in compare view

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[dependabot-preview[bot]]

Superseded by #17.