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

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https://hg.mozilla.org/integration/gaia-central/rev/84f413a40a6c
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #19390 from crdlc/bug-1012692

Bug 1012692 - (vertical-homescreen) Add option to change the wallpaper

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https://hg.mozilla.org/integration/gaia-central/rev/f65c2bee6705
Author: crdlc <crdlc@tid.es>
Desc: Bug 1012692 - (vertical-homescreen) Add option to change the wallpaper
Bumping manifests a=b2g-bump