fetch calls with anything but a request object will execute without the x-amzn-trace-id header

[berndfuhrmann]

Consider this code

import AWSXRay from 'aws-xray-sdk-core';
import { captureFetchGlobal } from 'aws-xray-sdk-fetch';

captureFetchGlobal();

var segment = new AWSXRay.Segment('test');
var ns = AWSXRay.getNamespace();

ns.run(async function () {
  AWSXRay.setSegment(segment);
  fetch('http://localhost:3000')
  segment.close();
});

I would expect localhost:3000 to receive the x-amzn-trace-id header, but it doesn't.
When changing the fetch call like this: fetch(new Request("http://localhost:3000")); it works.
Working on a PR to fix this.