message: docs(lettable-operators): example of own operators
diff: @@ -78,13 +78,13 @@ You, in fact, could _always_ do this with `let`... but building your own operato
  ```ts
  import { interval } from 'rxjs/observable/interval';
  -import { map, take, toArray } from 'rxjs/operators';
  +import { filter, map, take, toArray } from 'rxjs/operators';
  /**
  * an operator that takes every Nth value
  */
  const takeEveryNth = (n: number) => <T>(source: Observable<T>) =>
  - new Observable(observer => {
  + new Observable<T>(observer => {
  let count = 0;
  return source.subscribe({
  next(x) {
  @@ -95,11 +95,13 @@ const takeEveryNth = (n: number) => <T>(source: Observable<T>) =>
  })
  });
  +const takeEveryNthSimple = (n: number) => <T>(source: Observable<T>) =>
  + source.pipe(filter((value, index) => index % n === 0 ))
  interval(1000).pipe(
  takeEveryNth(2),
  map(x => x + x),
  - takeEveryNth(3),
  + takeEveryNthSimple(3),
  take(3),
  toArray()
  )
  