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

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https://hg.mozilla.org/integration/gaia-central/rev/ac2ad84f3387
Author: Fabrice Desré <fabrice@desre.org>
Desc: Merge pull request #21726 from ngokevin/master

Bug 1011016; new marketplace dev/stage packages

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https://hg.mozilla.org/integration/gaia-central/rev/9f17a755b5df
Author: Kevin Ngo <ngoke@mozilla.com>
Desc: Bug 1011016; new marketplace dev/stage packages
Bumping manifests a=b2g-bump