Bumping gaia.json for 2 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/f6c1c9760150
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #16687 from flodolo/bug975637

Bug 975637 - [FTU] Make title in time zone selection completely localizable

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https://hg.mozilla.org/integration/gaia-central/rev/fc97bb32ac8c
Author: Francesco Lodolo (:flod) <flod@lodolo.net>
Desc: Bug 975637 - [FTU] Make title in time zone selection completely localizable
Tests added by :fcampo
Bumping manifests a=b2g-bump