Update README.md

Author: artdong

README.md

@@ -1,7 +1,7 @@
 # react-org-tree
 
 [![npm version][npm-image]][npm-url]
-[![mnt-image](https://img.shields.io/maintenance/yes/2020.svg)](../../commits/master)
+[![mnt-image](https://img.shields.io/maintenance/yes/2021.svg)](../../commits/master)
 [![GitHub stars](https://img.shields.io/github/stars/artdong/react-org-tree.svg)](https://github.com/artdong/react-org-tree/stargazers)
 [![GitHub forks](https://img.shields.io/github/forks/artdong/react-org-tree.svg)](https://github.com/artdong/react-org-tree/network)
 [![GitHub license](https://img.shields.io/badge/license-MIT-blue.svg)](https://github.com/artdong/react-org-tree/blob/master/LICENSE)