Fix extra byte in websocket binary frame on EIO v3

In v3 of the engine.io protocol, the packet type byte is prepended to
the binary data that is sent out on a websocket binary frame.  This byte
needs to be stripped off the data before it's sent to the handler.

Closes #277.

Author: kelnos

engineioxide/src/transport/ws.rs

@@ -182,7 +182,11 @@ where
                 }
                 p => return Err(Error::BadPacket(p)),
             },
-            Message::Binary(data) => {
+            Message::Binary(mut data) => {
+                if socket.protocol == ProtocolVersion::V3 && !data.is_empty() {
+                    // The first byte is the message type, which we don't need.
+                    let _ = data.remove(0);
+                }
                 engine.handler.on_binary(data, socket.clone());
                 Ok(())
             }