Update embedded-io requirement from 0.5.0 to 0.6.0

Updates the requirements on [embedded-io](https://github.com/rust-embedded/embedded-hal) to permit the latest version.
- [Release notes](https://github.com/rust-embedded/embedded-hal/releases)
- [Commits](rust-embedded/embedded-hal@embedded-io-v0.5.0...embedded-io-v0.6.0)

---
updated-dependencies:
- dependency-name: embedded-io
  dependency-type: direct:production
...

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

capnp/Cargo.toml

@@ -17,7 +17,7 @@ keywords = ["encoding", "protocol", "serialization"]
 [dependencies]
 quickcheck = { version = "1", optional = true }
 
-embedded-io = { version = "0.5.0", default-features = false, optional = true }
+embedded-io = { version = "0.6.0", default-features = false, optional = true }
 
 [dev-dependencies]
 quickcheck = "1"