Merge pull request zendframework/zendframework#2135 from Thinkscape/h…

…otfix/callable-not-callback

Change all 'callback' typehints to 'callable'

src/Server.php

@@ -171,8 +171,8 @@ public function __call($method, $params)
      * any arguments following the namespace will be aggregated and passed at
      * dispatch time.
      *
-     * @param string|array $function Valid callback
-     * @param string $namespace Optional namespace prefix
+     * @param string|array|callable $function  Valid callback
+     * @param string                $namespace Optional namespace prefix
      * @return void
      * @throws Zend\XmlRpc\Server\Exception
      */