fetch not available

[TimDaub]

related to: lukechilds/browser-env#82

According to fetch spec, it's available under WindowOrWorkerGlobalScope.

related: jsdom/jsdom#1724

[TimDaub]

This is still a problem, e.g. when adding the window module to an ava test setup:

const Window = require('window');
global.window = new Window();

and in package.json

"ava": {
  "require": ["./test/_window.js"]
}