使用thinkphp 5.1的migration时定义了down方法还提示No migrations to rollback？

Question

学习使用tp5的数据迁移，在类中定义了up和down方法，在命令行执行php think migrate:run可以按预期执行，但是在执行php think migrate:rollback时提示No migrations to rollback

截图：

实现代码如下：

<?php

use think\migration\Migrator;
use think\migration\db\Column;
use Phinx\Db\Adapter\MysqlAdapter;

class BannerModifyField extends Migrator
{
    /**
     * Change Method.
     *
     * Write your reversible migrations using this method.
     *
     * More information on writing migrations is available here:
     * http://docs.phinx.org/en/latest/migrations.html#the-abstractmigration-class
     *
     * The following commands can be used in this method and Phinx will
     * automatically reverse them when rolling back:
     *
     *    createTable
     *    renameTable
     *    addColumn
     *    renameColumn
     *    addIndex
     *    addForeignKey
     *
     * Remember to call "create()" or "update()" and NOT "save()" when working
     * with the Table class.
     */
    public function up()
    {
        $table = $this->table('banner',array('engine'=>'Innodb'));
        $table->changeColumn('create_time', 'integer',array('limit' => MysqlAdapter::INT_REGULAR, 'signed'=>false, 'comment'=>'创建时间'))
              ->changeColumn('update_time', 'integer',array('limit' => MysqlAdapter::INT_REGULAR, 'signed'=>false, 'comment'=>'修改时间'))
              ->update();
    }

    public function down()
    {
        $table = $this->table('banner',array('engine'=>'Innodb'));
        $table->changeColumn('create_time', 'integer',array('limit' => MysqlAdapter::INT_REGULAR, 'comment'=>'创建时间'))
              ->changeColumn('update_time', 'integer',array('limit' => MysqlAdapter::INT_REGULAR, 'comment'=>'修改时间'))
              ->update();
    }
}

请大神指点，谢谢啦~