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/ab303aebb061
Author: Dominic Kuo <dkuo@mozilla.com>
Desc: Merge pull request #14075 from dominickuo/bug-911108-new

Bug 911108 - [music] change the hash and option to mix page when the player is reset by the storages, r=huchengtw-moz(cherry picked from commit 2758561ca39d2d2c30a4425f087515284b6c095f)