Fixes IE array detection

toString.call([]) fails while the Object.prototype.toString.call([]) works

lib/rsvp/all.js

@@ -3,9 +3,10 @@
 import { Promise } from "./promise";
 
 function all(promises) {
-  if(toString.call(promises) !== "[object Array]") {
+  if (Object.prototype.toString.call(promises) !== "[object Array]") {
     throw new TypeError('You must pass an array to all.');
   }
+
   return new Promise(function(resolve, reject) {
     var results = [], remaining = promises.length,
     promise;