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

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https://hg.mozilla.org/integration/gaia-central/rev/4d18ecb3653e
Author: James Graham <james@hoppipolla.co.uk>
Desc: Bug 1037450 - Don't package tests with gaiatest code for PyPI. r=dhunt

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https://hg.mozilla.org/integration/gaia-central/rev/400b0436d7b0
Author: Chris Lord <chrislord.net@gmail.com>
Desc: Merge pull request #21856 from Cwiiis/bug1038185-close-utility-tray-transition

Bug 1038185 - Fix transition when closing utility tray. r=etienne

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https://hg.mozilla.org/integration/gaia-central/rev/1bb939a9e464
Author: Chris Lord <chrislord.net@gmail.com>
Desc: Bug 1038185 - Fix transition when closing utility tray. r=etienne
Bumping manifests a=b2g-bump