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

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https://hg.mozilla.org/integration/gaia-central/rev/fb342e5c57e0
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Merge pull request #13080 from Rik/tabbar-overlays-modals-924256

Bug 924256 - The bottom panel tabbar overlays MMI screen and phone suggestion r=etienne

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https://hg.mozilla.org/integration/gaia-central/rev/ff28cef1e28d
Author: Anthony Ricaud <anthony@ricaud.me>
Desc: Bug 924256 - The bottom panel tabbar overlays MMI screen and phone suggestions screen