Polyfill fetch

Summary: Provide server add-on writers with a well-known fetch API

Reviewed By: mweststrate

Differential Revision: D34447630

fbshipit-source-id: 70386940c12f9e53aa97b3530a7edf1d40b5f2e2

desktop/flipper-server-core/src/FlipperServerImpl.tsx

@@ -7,6 +7,7 @@
  * @format
  */
 
+import './utils/fetch-polyfill';
 import EventEmitter from 'events';
 import {ServerController} from './comms/ServerController';
 import {CertificateExchangeMedium} from './utils/CertificateProvider';