Use is_iterable() function when possible

Finder.php

@@ -669,7 +669,7 @@ public function append($iterator)
             $this->iterators[] = $iterator->getIterator();
         } elseif ($iterator instanceof \Iterator) {
             $this->iterators[] = $iterator;
-        } elseif ($iterator instanceof \Traversable || \is_array($iterator)) {
+        } elseif (is_iterable($iterator)) {
             $it = new \ArrayIterator();
             foreach ($iterator as $file) {
                 $file = $file instanceof \SplFileInfo ? $file : new \SplFileInfo($file);