Bump base64 from 0.13.1 to 0.21.0

Bumps [base64](https://github.com/marshallpierce/rust-base64) from 0.13.1 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@v0.13.1...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

@@ -45,7 +45,7 @@ std = [
 # not, or if things are sketchy, please leave a comment next to it.
 arrayvec = { version = "0.7.2", default-features = false }
 atomic = { version = "0.5.1", default-features = false }
-base64 = { version = "0.13.1", default-features = false, features = ["alloc"] }
+base64 = { version = "0.21.0", default-features = false, features = ["alloc"] }
 bip39 = { version = "1.0.1", default-features = false }
 blake2-rfc = { version = "0.2.18", default-features = false }
 bs58 = { version = "0.4.0", default-features = false, features = ["alloc"] }