TP5 Fatal error: Class 'think\Route' not found

1、使用验证码了时：使用Composer安装think-captcha扩展包：

composer require topthink/think-captcha

报错：Fatal error: Class 'Route' not found in D:\WWW\JVS\tp5\vendor\topthink\think-captcha\src\helper.php on line 12

查看代码：

<?php
// +----------------------------------------------------------------------
// | ThinkPHP [ WE CAN DO IT JUST THINK ]
// +----------------------------------------------------------------------
// | Copyright (c) 2006-2015 http://thinkphp.cn All rights reserved.
// +----------------------------------------------------------------------
// | Licensed ( http://www.apache.org/licenses/LICENSE-2.0 )
// +----------------------------------------------------------------------
// | Author: yunwuxin <448901948@qq.com>
// +----------------------------------------------------------------------

Route::get('captcha/[:id]', "\\think\\captcha\\CaptchaController@index");

Validate::extend('captcha', function ($value, $id = '') {
    return captcha_check($value, $id);
});

Validate::setTypeMsg('captcha', ':attribute错误!');

修改为：

<?php
// +----------------------------------------------------------------------
// | ThinkPHP [ WE CAN DO IT JUST THINK ]
// +----------------------------------------------------------------------
// | Copyright (c) 2006-2015 http://thinkphp.cn All rights reserved.
// +----------------------------------------------------------------------
// | Licensed ( http://www.apache.org/licenses/LICENSE-2.0 )
// +----------------------------------------------------------------------
// | Author: yunwuxin <448901948@qq.com>
// +----------------------------------------------------------------------

\think\Route::get('captcha/[:id]', "\\think\\captcha\\CaptchaController@index");

\think\Validate::extend('captcha', function ($value, $id = "") {
    return captcha_check($value, $id, (array)\think\Config::get('captcha'));
});

\think\Validate::setTypeMsg('captcha', '验证码错误!');

就可以访问了。