[feat] Detect React-Native environment and use all websocket features (#591)

React-Native provides a Websocket object that is more functionally aligned with the Node.js websocket than the browser websocket.

It has the same constructor signature as the Node.js websocket and can support extraHeaders and protocols.

This PR will detect when the engine.io-client is running in React-Native, call the proper Websocket constructor, and enable support for extraHeaders.