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

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https://hg.mozilla.org/integration/gaia-central/rev/3d3d6183911f
Author: Yuren Ju <yurenju@gmail.com>
Desc: Merge pull request #15393 from yurenju/bug955887

Bug 955887 -  [Buri] "Add Collection" wallpaper label missing r=@timdream

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https://hg.mozilla.org/integration/gaia-central/rev/a63d2ee4ad43
Author: Yuren Ju <yurenju@gmail.com>
Desc: Bug 955887 -  [Buri] "Add Collection" wallpaper label missing

the root cause is we didn't use foo.en-US.properties for en-US instead
of en-US/apps/foo/foo.properties if GAIA_CONCAT_LOCALES=1, so we need to
use the original file in gaia directory not in locale basedir.