v1.6.20

Bump github.com/slack-go/slack from 0.9.5 to 0.10.0 (#61)

Bumps [github.com/slack-go/slack](https://github.com/slack-go/slack) from 0.9.5 to 0.10.0.
- [Release notes](https://github.com/slack-go/slack/releases)
- [Changelog](https://github.com/slack-go/slack/blob/master/CHANGELOG.md)
- [Commits](https://github.com/slack-go/slack/compare/v0.9.5...v0.10.0)

---
updated-dependencies:
- dependency-name: github.com/slack-go/slack
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>