message: docs(common): update ngForTrackBy error URL
  Old URL is redirected to
  `https://angular.io/api/common/NgForOf#!#change-propagation`
  which is not exactly
  `https://angular.io/api/common/NgForOf#change-propagation`
  PR Close
diff: @@ -155,7 +155,7 @@ export class NgForOf<T, U extends NgIterable<T> = NgIterable<T>> implements DoCh
  if (<any>console && <any>console.warn) {
  console.warn(
  `trackBy must be a function, but received ${JSON.stringify(fn)}. ` +
  - `See https://angular.io/docs/ts/latest/api/common/index/NgFor-directive.html#!#change-propagation for more information.`);
  + `See https://angular.io/api/common/NgForOf#change-propagation for more information.`);
  }
  }
  this._trackByFn = fn;
  