message: mistake on description for demo
  the demo shows that when 2 is emitted, an error throws, but description says 13. Maybe it's an previous version -.-
diff: @@ -30,7 +30,7 @@ import { Subscriber } from '../Subscriber';
  *
  * ---
  *
  - * ### Map and flatten numbers to the sequence 'a', 'b', 'c', but throw an error for 13
  + * ### Map and flatten numbers to the sequence 'a', 'b', 'c', but throw an error for 2
  * ```javascript
  * import { throwError, interval, of } from 'rxjs';
  * import { mergeMap } from 'rxjs/operators';
  