Revert "Index: fix twitter handle"

Author: yuwata

content/_index.md

@@ -10,7 +10,7 @@ BookToC: false
 The userspace API ("uapi") group is a community for people with an interest in innovating how we build, deploy, and run modern Linux operating systems.
 It serves as a central gathering place for specs, documentation, and ideas.
 
-Follow [@uapi-group](https://twitter.com/uapi-group) on twitter to catch the latest news!
+Follow [@uapi-group](https://twitter.com/uapi_group) on twitter to catch the latest news!
 
 ## UAPI Group Specifications