fix(typings): relax throttle selector type

spec/operators/throttle-spec.ts

@@ -2,6 +2,7 @@ import { expect } from 'chai';
 import * as Rx from '../../src/Rx';
 import marbleTestingSignature = require('../helpers/marble-testing'); // tslint:disable-line:no-require-imports
 
+declare const type;
 declare const { asDiagram };
 declare const hot: typeof marbleTestingSignature.hot;
 declare const cold: typeof marbleTestingSignature.cold;
@@ -338,6 +339,22 @@ describe('Observable.prototype.throttle', () =>  {
     );
   });
 
+  type('should support selectors of the same type', () => {
+    /* tslint:disable:no-unused-variable */
+    let o: Rx.Observable<number>;
+    let s: Rx.Observable<number>;
+    let r: Rx.Observable<number> = o.throttle((n) => s);
+    /* tslint:enable:no-unused-variable */
+  });
+
+  type('should support selectors of a different type', () => {
+    /* tslint:disable:no-unused-variable */
+    let o: Rx.Observable<number>;
+    let s: Rx.Observable<string>;
+    let r: Rx.Observable<number> = o.throttle((n) => s);
+    /* tslint:enable:no-unused-variable */
+  });
+
   describe('throttle(fn, { leading: true, trailing: true })', () => {
     asDiagram('throttle(fn, { leading: true, trailing: true })')('should immediately emit the first value in each time window', () =>  {
       const e1 =   hot('-a-xy-----b--x--cxxx--|');

src/internal/operators/throttle.ts

@@ -59,13 +59,13 @@ export const defaultThrottleConfig: ThrottleConfig = {
  * @method throttle
  * @owner Observable
  */
-export function throttle<T>(durationSelector: (value: T) => SubscribableOrPromise<number>,
+export function throttle<T>(durationSelector: (value: T) => SubscribableOrPromise<any>,
                             config: ThrottleConfig = defaultThrottleConfig): MonoTypeOperatorFunction<T> {
   return (source: Observable<T>) => source.lift(new ThrottleOperator(durationSelector, config.leading, config.trailing));
 }
 
 class ThrottleOperator<T> implements Operator<T, T> {
-  constructor(private durationSelector: (value: T) => SubscribableOrPromise<number>,
+  constructor(private durationSelector: (value: T) => SubscribableOrPromise<any>,
               private leading: boolean,
               private trailing: boolean) {
   }
@@ -88,7 +88,7 @@ class ThrottleSubscriber<T, R> extends OuterSubscriber<T, R> {
   private _hasTrailingValue = false;
 
   constructor(protected destination: Subscriber<T>,
-              private durationSelector: (value: T) => SubscribableOrPromise<number>,
+              private durationSelector: (value: T) => SubscribableOrPromise<any>,
               private _leading: boolean,
               private _trailing: boolean) {
     super(destination);

src/internal/patching/operator/throttle.ts

@@ -42,7 +42,7 @@ import { throttle as higherOrder, ThrottleConfig, defaultThrottleConfig } from '
  * @owner Observable
  */
 export function throttle<T>(this: Observable<T>,
-                            durationSelector: (value: T) => SubscribableOrPromise<number>,
+                            durationSelector: (value: T) => SubscribableOrPromise<any>,
                             config: ThrottleConfig = defaultThrottleConfig): Observable<T> {
   return higherOrder(durationSelector, config)(this);
 }