simplified extension check in classmap generation

src/Composer/Autoload/ClassMapGenerator.php

@@ -66,9 +66,10 @@ class ClassMapGenerator
         $map = array();
 
         foreach ($path as $file) {
+            /** @var \SplFileInfo $file */
             $filePath = $file->getRealPath();
 
-            if (!in_array(pathinfo($filePath, PATHINFO_EXTENSION), array('php', 'inc'))) {
+            if (!in_array($file->getExtension(), array('php', 'inc'))) {
                 continue;
             }