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

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https://hg.mozilla.org/integration/gaia-central/rev/4073a9939e89
Author: Justin D'Arcangelo <justindarc@gmail.com>
Desc: Merge pull request #15876 from justindarc/bug957709

Patch to throttle launching of Gallery activity (Bug 957709)

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https://hg.mozilla.org/integration/gaia-central/rev/5565cefafd9e
Author: Justin D'Arcangelo <justindarc@gmail.com>
Desc: Patch to throttle launching of Gallery activity (Bug 957709)

Patched Gallery for 1.4.
Bumping manifests a=b2g-bump