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

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https://hg.mozilla.org/integration/gaia-central/rev/ebb5ed73230a
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Merge pull request #15217 from Moz-TedC/master

Bug 953041 - Adding English, Chinese, and French translations for "skip" button, r=timdream

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https://hg.mozilla.org/integration/gaia-central/rev/28afade16a7f
Author: Moz-TedC <tclancy@mozilla.com>
Desc: Bug 953041 - Adding English, Chinese, and French translations for "skip" button.

Translations were copied from a visually-similar part of the FTU app (gaia/apps/communications/ftu/locales). There's no Arabic translation yet.