Fix Array.prototype.{reduce,reduceRight} to pass undefined as receiver

src/array.js

Index: src/array.js
diff --git a/src/array.js b/src/array.js
index 6cf417874da2924caf1477be658cefb408bfc3bc..34ebd4e227fc5fdc23656b38091d8dbe4f9b52cc 100644
--- a/src/array.js
+++ b/src/array.js
@@ -1252,7 +1252,7 @@ function ArrayReduce(callback, current) {
   for (; i < length; i++) {
     var element = this[i];
     if (!IS_UNDEFINED(element) || i in this) {
-      current = callback.call(null, current, element, i, this);
+      current = callback.call(void 0, current, element, i, this);
     }
   }
   return current;
@@ -1283,7 +1283,7 @@ function ArrayReduceRight(callback, current) {
   for (; i >= 0; i--) {
     var element = this[i];
     if (!IS_UNDEFINED(element) || i in this) {
-      current = callback.call(null, current, element, i, this);
+      current = callback.call(void 0, current, element, i, this);
     }
   }
   return current;