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

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https://hg.mozilla.org/integration/gaia-central/rev/5da7f54181fd
Author: Chris Lord <chrislord.net@gmail.com>
Desc: Merge pull request #21806 from Cwiiis/fixed-position-utility-tray

Bug 984797 - Fixed position utility tray. r=etienne

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https://hg.mozilla.org/integration/gaia-central/rev/bb831eb56c06
Author: Chris Lord <chrislord.net@gmail.com>
Desc: Bug 984797 - Fixed-position utility tray. r=etienne
Bumping manifests a=b2g-bump