Should match's return type be void?

Shouldn't the return type of [match](https://github.com/Havvy/result/blob/master/result.js.flow#L32), and by extension the `MatchBlock` type, be polymorphic?

```js
type MatchBlock<R, T, F> = {
  Ok(value: T): R;
  Fail(failure: F): R;
}
// ...
match(block: MatchBlock<R, T, F>): R;