message: docs(windowWhen): fix example
diff: @@ -28,13 +28,13 @@ import { OperatorFunction } from '../types';
  * Emit only the first two clicks events in every window of [1-5] random seconds
  * ```javascript
  * import { fromEvent, interval } from 'rxjs';
  - * import { windowWhen, map, mergeAll } from 'rxjs/operators';
  + * import { windowWhen, map, mergeAll, take } from 'rxjs/operators';
  *
  * const clicks = fromEvent(document, 'click');
  * const result = clicks.pipe(
  * windowWhen(() => interval(1000 + Math.random() * 4000)),
  * map(win => win.pipe(take(2))), // each window has at most 2 emissions
  - * mergeAll(), // flatten the Observable-of-Observables
  + * mergeAll() // flatten the Observable-of-Observables
  * );
  * result.subscribe(x => console.log(x));
  * ```
  