message: Fallback to global fetch is `Orbit.fetch` is not defined
diff: @@ -18,10 +18,6 @@ import { PullOperator, PullOperators } from './lib/pull-operators';
  import { getTransformRequests, TransformRequestProcessors } from './lib/transform-requests';
  import { InvalidServerResponse } from './lib/exceptions';
  -if (typeof Orbit.globals.fetch !== 'undefined' && Orbit.fetch === undefined) {
  - Orbit.fetch = Orbit.globals.fetch.bind(Orbit.globals);
  -}
  -
  export interface FetchSettings {
  headers?: object;
  method?: string;
  @@ -165,7 +161,7 @@ export default class JSONAPISource extends Source implements Pullable, Pushable
  }
  // console.log('fetch', fullUrl, mergedSettings, 'polyfill', fetch.polyfill);
  -
  + let fetchFn = Orbit.fetch || fetch;
  if (settings.timeout) {
  let timeout = settings.timeout;
  delete settings.timeout;
  @@ -178,7 +174,7 @@ export default class JSONAPISource extends Source implements Pullable, Pushable
  reject(new NetworkError(`No fetch response within ${timeout}ms.`));
  }, timeout);
  - Orbit.fetch(fullUrl, settings)
  + fetchFn(fullUrl, settings)
  .catch(e => {
  Orbit.globals.clearTimeout(timer);
  @@ -196,7 +192,7 @@ export default class JSONAPISource extends Source implements Pullable, Pushable
  .then(resolve, reject);
  });
  } else {
  - return Orbit.fetch(fullUrl, settings)
  + return fetchFn(fullUrl, settings)
  .catch(e => this.handleFetchError(e))
  .then(response => this.handleFetchResponse(response));
  }
  