Add return type declaration to compile method in AssetsNode

Author: c15k0

src/base/extension/AssetsNode.php

@@ -28,7 +28,7 @@ public function __construct($name, $values, $line, $type = 'js')
         $this->type = $type;
     }
 
-    public function compile(Compiler $compiler)
+    public function compile(Compiler $compiler): void
     {
         $scripts = $this->getNode("scripts");