_on_open(ws) {
        // Create and attach HyperExpress.Websocket polyfill component to uWS websocket
        ws.poly = new Websocket(ws);

        // Trigger WebsocketRoute handler on new connection open so user can listen for events
        this.handler(ws.poly);
    }
Handles 'open' event from uWebsockets.js
@private
@param {uWS.Websocket} ws