Update reddsa requirement from 0.3.0 to 0.4.0

Updates the requirements on [reddsa](https://github.com/ZcashFoundation/reddsa) to permit the latest version.
- [Release notes](https://github.com/ZcashFoundation/reddsa/releases)
- [Changelog](https://github.com/ZcashFoundation/reddsa/blob/main/CHANGELOG.md)
- [Commits](https://github.com/ZcashFoundation/reddsa/compare/0.3.0...0.4.0)

---
updated-dependencies:
- dependency-name: reddsa
  dependency-type: direct:production
...

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

Cargo.toml

@@ -17,7 +17,7 @@ description = "A standalone implementation of the RedJubjub signature scheme."
 features = ["nightly"]
 
 [dependencies]
-reddsa = "0.3.0"
+reddsa = "0.4.0"
 rand_core = "0.6"
 serde = { version = "1", optional = true, features = ["derive"] }
 thiserror = "1.0"