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

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https://hg.mozilla.org/integration/gaia-central/rev/6bf2a9a87dba
Author: Rudy Lu <me@rudy.lu>
Desc: Merge pull request #14488 from RudyLu/keyboard/Bug888253-keyboard_settings_migration

 Bug 888253 - Settings data migration for keyboard layouts.
r=gnarf, gary, yuren

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https://hg.mozilla.org/integration/gaia-central/rev/73762b06166b
Author: Rudy Lu <me@rudy.lu>
Desc:  Bug 888253 - Settings data migration for keyboard layouts