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

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https://hg.mozilla.org/integration/gaia-central/rev/e07e3027a2fa
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #12144 from mpizza/Bug_908846_tablet_wallpaper

Bug_908846 - Add New Wallpapers for 1.2 for Tablet, r=fred

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https://hg.mozilla.org/integration/gaia-central/rev/e7657e750f3e
Author: GaryChen(pychen) <mmm198219@gmail.com>
Desc: Bug_908846 - Add New Wallpapers for 1.2 for Tablet
    remove old images