chore(deps): bump base64 from 0.20.0 to 0.21.0 (#279)

Bumps [base64](https://github.com/marshallpierce/rust-base64) from 0.20.0 to 0.21.0.
- [Release notes](https://github.com/marshallpierce/rust-base64/releases)
- [Changelog](https://github.com/marshallpierce/rust-base64/blob/master/RELEASE-NOTES.md)
- [Commits](https://github.com/marshallpierce/rust-base64/compare/v0.20.0...v0.21.0)

---
updated-dependencies:
- dependency-name: base64
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Cargo.toml

@@ -27,7 +27,7 @@ env_logger = "0.10"
 parking_lot = "0.12.1"
 hmac = "0.12"
 sha2 = "0.10"
-base64 = "0.20"
+base64 = "0.21"
 stringprep = "0.1"
 tokio-rustls = "0.23"
 rustls-pemfile = "1"