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

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https://hg.mozilla.org/integration/gaia-central/rev/adca2c1cea8e
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Merge pull request #13985 from pivanov/bug-939272

Bug 939272 - [Status Bar] Update to icons - Airplane Mode, Messages, Geolocation, Tethering, r=timdream

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https://hg.mozilla.org/integration/gaia-central/rev/d860f21fe198
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Bug 939272 - [Status Bar] Update to icons - Airplane Mode, Messages, Geolocation, Tethering