字符串最小长度验证

 {title}占位符，对应columns里面title

"title": [    
    {
      "type": "minlength",
      "required": false,
      "isAdd": true,
      "isEdit": true,
      "min": 10,
      "message": "【{title}】值最小长度为10。"
    }
  ],