Add jwcai and tianyuj to the owner's file of libs/ui

for the development of BufferHub project. OWNERS file is out of sync.
This change syncs the file and added jwcai and tianyuj to the OWNERS.

Bug: None
Test: None
Change-Id: I817d3dc323e46aa7417a583d1faa8e0bbb87c3df
1 file changed