Merge "Fix warnings in preparation for Rust 1.54.0"

        let headers = vec![

            quiche::h3::Header::new(b":status", b"200"),

            quiche::h3::Header::new(b"content-type", b"application/dns-message"),

            quiche::h3::Header::new(b"content-length", &len.to_string().as_bytes()),

            quiche::h3::Header::new(b"content-length", len.to_string().as_bytes()),

            // TODO: need to add cache-control?

        ];