public function update($id)
 {
     if (!empty($_POST["password"]) && $_POST["password"] != "********") {
         $password = Hash::make($_POST["password"]);
         DB::table('users')->where('id', $id)->update(array('password' => $password));
     }
     if (!empty($_POST["limits"])) {
         $privileges = implode(",", $_POST["limits"]);
         DB::table('users')->where('id', $id)->update(array('privileges' => $privileges));
     }
     // 渲染界面
     return KTAnchor::flushLocation("更新完毕");
 }