message: docs(operators): fixing a typo
  There seems to be a typo in this doc,
  ... received so ~var~ -> ... received so _far_
diff: @@ -44,7 +44,7 @@ export function scan<V, A, S>(accumulator: (acc: A | S, value: V, index: number)
  * // Get the sum of the numbers coming in.
  * scan((total, n) => total + n),
  * // Get the average by dividing the sum by the total number
  - * // received so var (which is 1 more than the zero-based index).
  + * // received so far (which is 1 more than the zero-based index).
  * map((sum, index) => sum / (index + 1))
  * )
  * .subscribe(console.log);
  