fix ws subportocol lowercase header

src/handshake/client.rs

@@ -135,7 +135,12 @@ fn generate_request(request: Request, key: &str) -> Result<Vec<u8>> {
         key = key
     )
     .unwrap();
+
     for (k, v) in request.headers() {
+        let mut k = k.as_str();
+        if  k == "sec-websocket-protocol".to_string(){
+            k = "Sec-WebSocket-Protocol";
+        }
         writeln!(req, "{}: {}\r", k, v.to_str()?).unwrap();
     }
     writeln!(req, "\r").unwrap();