WebSocket not correctly polyfilled

[saba-abi]

In https://github.com/awslabs/amazon-kinesis-video-streams-webrtc-sdk-js/blob/master/src/SignalingClient.ts#L151

this.websocket = new (WebSocket || require('ws'))(signedURL);

When WebSocket is not defined, e.g. in Node.js, you will get a runtime error:

"ReferenceError: WebSocket is not defined"

The correct way to polyfill this would be:

const WS = (typeof WebSocket !== 'undefined') ? WebSocket : require('ws');
this.websocket = new WS(signedURL);