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

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https://hg.mozilla.org/integration/gaia-central/rev/3dc9f97f0061
Author: Sherman Chen <shamenchens@users.noreply.github.com>
Desc: Merge pull request #18835 from shamenchens/Bug1003771-Homescreen

Bug 1003771 Move distribution_tablet/homescreens.json to apps/homescreen/build/tablet/, r=yurenju

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https://hg.mozilla.org/integration/gaia-central/rev/8596654dcb7f
Author: Sherman Chen <shamen.chens@gmail.com>
Desc: Bug 1003771 Move distribution_tablet/homescreens.json to apps/homescreen/build/tablet/
Bumping manifests a=b2g-bump