update member list for sig/ddl, promote xiongjiwei to reviewer (#324)

Co-authored-by: Shirly <wuxuelian@pingcap.com>

special-interest-groups/sig-ddl/member-list.md

@@ -24,11 +24,11 @@
 - [spongedu](https://github.com/spongedu)
 - [Deardrops](https://github.com/Deardrops)
 - [xhebox](https://github.com/xhebox)
+- [xiongjiwei](https://github.com/xiongjiwei)
 
 ## Active Contributors
 
 - [reafans](https://github.com/reafans)
 - [Rustin-Liu](https://github.com/Rustin-Liu)
-- [xiongjiwei](https://github.com/xiongjiwei)
 - [wangggong](https://github.com/wangggong)
 - [zhaox1n](https://github.com/zhaox1n)