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

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https://hg.mozilla.org/integration/gaia-2_0/rev/4831c478975a
Author: Rudy Lu <me@rudy.lu>
Desc: Merge pull request #20520 from RudyLu/ime/Bug1013837_ime_menu_styleUpdate

Bug 1013837 - Adjust the style of ime menu.
r=timdream.
(cherry picked from commit 495bc911fc93bd6307869793d231c11d96169778)
a=bajaj.
Bumping manifests a=b2g-bump