fix(IteratorObservable): clarify the return type of IteratorObservabl…

…e.create()

BREAKING CHANGE - `IteratorObservable.create<T>()` now returns correctly
`Obsevable<T>` with supplied type parameter `T`. This fixes the previous
implmentations which always returns `Obsevable<{}>`.

src/observable/IteratorObservable.ts

@@ -13,7 +13,7 @@ import { Subscriber } from '../Subscriber';
 export class IteratorObservable<T> extends Observable<T> {
  private iterator: any;
 
- static create<T>(iterator: any, scheduler?: Scheduler) {
+ static create<T>(iterator: any, scheduler?: Scheduler): IteratorObservable<T> {
  return new IteratorObservable(iterator, scheduler);
  }