Bump base64 from 0.20.0 to 0.21.0

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](marshallpierce/rust-base64@v0.20.0...v0.21.0)

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

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

Author: dependabot[bot]

Cargo.lock

@@ -17,7 +17,7 @@ tokio = { version = "1.16", features = ["macros", "signal", "rt-multi-thread"] }
 dotenv = { version = "0.15.0" }
 serenity = "0.11.5"
 regex = "1.7.3"
-base64 = "0.20.0"
+base64 = "0.21.0"
 process_control = "4.0"
 cached = "0.42.0"
 lazy_static = "1.4.0"