Update erased-serde requirement from 0.3 to 0.4

Updates the requirements on [erased-serde](https://github.com/dtolnay/erased-serde) to permit the latest version.
- [Release notes](https://github.com/dtolnay/erased-serde/releases)
- [Commits](dtolnay/erased-serde@0.3.0...0.4.5)

---
updated-dependencies:
- dependency-name: erased-serde
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Cargo.toml

@@ -17,7 +17,7 @@ name = "stats"
 [dependencies]
 iobuffer = "0.2"
 serde = { version = "1.0", features = ["derive"] }
-erased-serde = "0.3"
+erased-serde = "0.4"
 serde_json = "1.0"
 slog = { version = "2.7", features = [ "nested-values" ] }
 slog-json = { version = "2.6", features = [ "nested-values" ] }