Bumping gaia.json for 3 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/96f78501506e
Author: Florin Strugariu <bebef_1987@yahoo.com>
Desc: Merge pull request #20508 from yzen/bug-1018214

Bug 1018214, Bug 1021710 - utility tray gaia-ui tests with some tweaks to hopefully avoid intermittents.

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https://hg.mozilla.org/integration/gaia-central/rev/a5013b317c2e
Author: Yura Zenevich <yzenevich@mozilla.com>
Desc: Bug 1021710 - updating accessibility.js to use standard marionette timeout instead of it's arbitrary one when retrieving an accessible object.

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https://hg.mozilla.org/integration/gaia-central/rev/24851c9a0c26
Author: Yura Zenevich <yzenevich@mozilla.com>
Desc: Bug 1018214 - adding a number of gaia ui tests for status bar and utility tray accessibility. r=Bebe
Bumping manifests a=b2g-bump