simplification using es6 syntax

lib/array.js

@@ -1,12 +1,12 @@
 'use strict';
 
 module.exports = {
-    toArray: arraylike => Array.prototype.slice.call(arraylike || []),
+    toArray: arraylike => [...arraylike],
 
     flatten: function flatten (ar) {
         return ar.reduce((acc, item) => {
             if (Array.isArray(item)) {
-                acc.push.apply(acc, flatten(item));
+                acc.push(...flatten(item));
             } else {
                 acc.push(item);
             }