Add droger as OWNER of google_apis/gaia

Change-Id: I28c5211f2a2c3334837cba02d4a051174c84e095
Reviewed-on: https://chromium-review.googlesource.com/1170701Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Commit-Queue: David Roger <droger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582148}

google_apis/gaia/OWNERS

+droger@chromium.org
 msarda@chromium.org
 rogerta@chromium.org
 zelidrag@chromium.org