add return annotation to promiseTimeout

Author: hawkrives

source/lib/promise-timeout.js

@@ -1,6 +1,6 @@
 // @flow
 
-export function promiseTimeout(ms: number, promise: Promise<any>) {
+export function promiseTimeout(ms: number, promise: Promise<any>): Promise<any> {
   return new Promise(function(resolve, reject) {
     // create a timeout to reject promise if not resolved
     let timer = setTimeout(function() {