Bumping gaia.json for 1 gaia-1_2 revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-1_2/rev/d273b1eabee3
Author: Ben Kelly <bkelly@mozilla.com>
Desc: Merge pull request #12835 from wanderview/shared-tvm-append

Bug 918179: Optimize append case in tag_visibility_monitor.  r=djf
(cherry picked from commit ea967f79e5f29e752b9abb4df14fc334946560a0)