- [ ] I have searched the [issues](https://github.com/vueComponent/ant-design-vue/issues) of this repository and believe that this is not a duplicate. ### Version 1.3.9 ### Environment 火狐,谷歌 IE11 ### Reproduction link [https://vue.ant.design/docs/vue/introduce/](https://vue.ant.design/docs/vue/introduce/) ### Steps to reproduce RangePicker组件mode为['month', 'month']的情况下起始月份和结束月份不能选择同一月份 ### What is expected? RangePicker组件mode为['month', 'month']的情况下起始月份和结束月份能选择同一月份 ### What is actually happening? RangePicker组件mode为['month', 'month']的情况下起始月份和结束月份不能选择同一月份 <!-- generated by issue-helper. DO NOT REMOVE -->