fix(fromPromise): fix type signature

Author: luisgabriel

src/Observable.ts

@@ -140,7 +140,7 @@ export default class Observable<T> implements CoreOperators<T>  {
   static fromArray: <T>(array: T[], scheduler?: Scheduler) => Observable<T>;
   static fromEvent: <T>(element: any, eventName: string, selector: (...args:Array<any>) => T) => Observable<T>;
   static fromEventPattern: <T>(addHandler: (handler:Function)=>void, removeHandler: (handler:Function) => void, selector?: (...args:Array<any>) => T) => Observable<T>;
-  static fromPromise: <T>(promise: Promise<T>) => Observable<T>;
+  static fromPromise: <T>(promise: Promise<T>, scheduler?: Scheduler) => Observable<T>;
   static interval: (interval: number) => Observable<number>;
   static merge: (...observables:any[]) => Observable<any>;
   static never: <T>() => Observable<T>;

src/observables/PromiseObservable.ts

@@ -9,7 +9,7 @@ export default class PromiseObservable<T> extends Observable<T> {
   _isScalar: boolean = false;
   value: T;
 
-  static create<T>(promise: Promise<T>, scheduler: Scheduler = immediate) {
+  static create<T>(promise: Promise<T>, scheduler: Scheduler = immediate): Observable<T> {
     return new PromiseObservable(promise, scheduler);
   }