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

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https://hg.mozilla.org/integration/gaia-central/rev/5f1bb0739ef7
Author: Marcus Cavanaugh <m@mcav.com>
Desc: Merge pull request #19516 from mcav/async-send

Bug 921050 - Send email in the background. r=asuth

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https://hg.mozilla.org/integration/gaia-central/rev/cdb06337ef0d
Author: Marcus Cavanaugh <m@mcav.com>
Desc: Bug 921050 - Send email in the background.
Bumping manifests a=b2g-bump