Foreach is faster than array_map.

When connecting 500 routes, this method was taking 6ms on my machine.
Afterwards it takes 0.

src/Routing/Route/Route.php

@@ -155,7 +155,10 @@ public function extensions($extensions = null)
      */
     public function setExtensions(array $extensions)
     {
-        $this->_extensions = array_map('strtolower', $extensions);
+        $this->_extensions = [];
+        foreach ($extensions as $ext) {
+            $this->_extensions[] = strtolower($ext);
+        }
 
         return $this;
     }