Update spin requirement from 0.4.9 to 0.5.0 (#325)

Updates the requirements on [spin](https://github.com/mvdnes/spin-rs) to permit the latest version.
- [Release notes](https://github.com/mvdnes/spin-rs/releases)
- [Commits](https://github.com/mvdnes/spin-rs/commits)

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

Cargo.toml

@@ -20,7 +20,7 @@ codecov = { repository = "PyO3/pyo3", branch = "master", service = "github" }
 
 [dependencies]
 libc = "0.2.43"
-spin = "0.4.9"
+spin = "0.5.0"
 num-traits = "0.2.6"
 pyo3cls = { path = "pyo3cls", version = "=0.6.0-alpha.1" }
 mashup = "0.1.9"