Update serde_closure requirement from 0.2 to 0.3

Updates the requirements on [serde_closure](https://github.com/alecmocatta/serde_closure) to permit the latest version.
- [Release notes](https://github.com/alecmocatta/serde_closure/releases)
- [Commits](alecmocatta/serde_closure@v0.2.0...v0.3.0)

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

Cargo.toml

@@ -58,7 +58,7 @@ palaver = "0.3.0-alpha.2"
 pin-utils = "0.1.0-alpha.4"
 rand = "0.7"
 serde = { version = "1.0", features = ["derive"] }
-serde_closure = "0.2"
+serde_closure = "0.3"
 serde_traitobject = "0.2"
 serde_json = { version = "1.0", features = ["unbounded_depth"] }
 serde_pipe = "0.1"