Add nigeltao@chromium.org to app_service/OWNERS

Change-Id: I6972a8214f1402f21efe8f7afa35c8f135c996d0
Reviewed-on: https://chromium-review.googlesource.com/c/1351976Reviewed-by: Dominick Ng <dominickn@chromium.org>
Commit-Queue: Nigel Tao <nigeltao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612437}

chrome/services/app_service/OWNERS

 benwells@chromium.org
 dominickn@chromium.org
+nigeltao@chromium.org
 
 per-file manifest.json=set noparent
 per-file manifest.json=file://ipc/SECURITY_OWNERS