[owners] Ensure OWNERS file ends with newline in //third_party

Some OWNERS file ends with a newline character, some don't. As
text editor tends to add newline at the end of text files when
saving, normalize all OWNERS files to end with a newline '\n'.

Bug: none
Change-Id: Id1f8897de75f4feb142459baa6f328a8c3f0bddd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2905780


Reviewed-by: Mike Pinkerton <pinkerton@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#886225}