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

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https://hg.mozilla.org/integration/gaia-central/rev/991402cd93d6
Author: Ran Ben Aharon <ran@everything.me>
Desc: Merge pull request #12634 from EverythingMe/911544-offline-ready

Bug 911544 - [e.me][feature] Support offline-ready [r=crdlc]

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https://hg.mozilla.org/integration/gaia-central/rev/7e280031920d
Author: Ran Ben Aharon <ran@ranbena.com>
Desc: Bug 911544 - [e.me][feature] Support offline-ready [r=crdlc]