update phpdoc block

Author: JBlond

lib/Diff.php

@@ -99,7 +99,8 @@ public function __construct($a, $b, $options=array())
 	/**
 	 * Render a diff using the supplied rendering class and return it.
 	 *
-	 * @param object $renderer An instance of the rendering object to use for generating the diff.
+	 * @param \Diff_Renderer_Abstract|object $renderer An instance of the rendering object to use for generating the diff.
+	 *
 	 * @return mixed The generated diff. Exact return value depends on the rendered.
 	 */
 	public function render(Diff_Renderer_Abstract $renderer)