Update tokio-tungstenite requirement in /hello-websocket-rust

Updates the requirements on [tokio-tungstenite](https://github.com/snapview/tokio-tungstenite) to permit the latest version.
- [Changelog](https://github.com/snapview/tokio-tungstenite/blob/master/CHANGELOG.md)
- [Commits](snapview/tokio-tungstenite@v0.20.1...v0.21.0)

---
updated-dependencies:
- dependency-name: tokio-tungstenite
  dependency-type: direct:production
...

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

Author: dependabot[bot]

hello-websocket-rust/Cargo.toml

@@ -9,7 +9,7 @@ edition = "2018"
 futures-channel = "0.3"
 futures-util = { version = "0.3", default-features = false, features = ["sink", "std"] }
 tokio = { version = "1.23.0",  features = ["full"] }
-tokio-tungstenite = "0.20.1"
+tokio-tungstenite = "0.21.0"
 tungstenite = "0.21.0"
 url = "2.4.1"