Bump github.com/mediocregopher/radix/v4 from 4.0.0-beta.1 to 4.0.0 (#460)

Bumps [github.com/mediocregopher/radix/v4](https://github.com/mediocregopher/radix) from 4.0.0-beta.1 to 4.0.0.
- [Release notes](https://github.com/mediocregopher/radix/releases)
- [Changelog](https://github.com/mediocregopher/radix/blob/v4.0.0/CHANGELOG.md)
- [Commits](https://github.com/mediocregopher/radix/compare/v4.0.0-beta.1...v4.0.0

)

---
updated-dependencies:
- dependency-name: github.com/mediocregopher/radix/v4
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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