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

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https://hg.mozilla.org/integration/gaia-central/rev/4073b397d7b5
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #20906 from guilherme-pg/bug947985-fmd-icon

Bug 947985 - Include final icon for Find My Device.

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https://hg.mozilla.org/integration/gaia-central/rev/7938357322c0
Author: Guilherme Goncalves <guilherme.p.gonc@gmail.com>
Desc: Bug 947985 - Include final icon for Find My Device.
Bumping manifests a=b2g-bump