dubbo -admin 无法注册到nacos

### Environment

* Dubbo Admin version: 0.4.0
* Java version: 1.8.0_301
* nacos server version: 2.0.3

### Steps to reproduce this issue

1. dubbo-admin-server模块使用的nacos-client版本是2.0.2，启动时无法注册到nacos，把nacos-client版本升级到2.0.3还是没办法注册，改成1.4.2版本就可以成功注册上去

Start in the dubbo-admin-server module and inspect its nacos-client dependency and startup registration path. Reproduce with Nacos server 2.0.3 using client versions 2.0.2 and 2.0.3, compare with 1.4.2, and consider the issue resolved when the supported 2.x client registers successfully.

Written by the indexing model from the issue text.