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

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https://hg.mozilla.org/integration/gaia-central/rev/4ff387ba1fbb
Author: Eitan Isaacson <eitan@monotonous.org>
Desc: Merge pull request #12282 from eeejay/bug-917586

Bug 917586 - Use newer version of screen reader simulator in desktop firefox. r=kgrandon

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https://hg.mozilla.org/integration/gaia-central/rev/467adffea105
Author: Eitan Isaacson <eitan@monotonous.org>
Desc: Bug 917586 - Use newer version of screen reader simulator in desktop firefox.