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

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https://hg.mozilla.org/integration/gaia-central/rev/3f3d1359afa3
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Merge pull request #14354 from timdream/wallpaper-size

Bug 945098 - Don't hardcode HVGA in wallpaper selection, r=arthurcc, r=crdlc

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https://hg.mozilla.org/integration/gaia-central/rev/678703a42de0
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Bug 945098 - Don't hardcode HVGA in wallpaper selection