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

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https://hg.mozilla.org/integration/gaia-2_1/rev/788a6ab570b8
Author: Ryan VanderMeulen <ryanvm@gmail.com>
Desc: Merge pull request #26926 from 6a68/bug-1087441-v2.1

Bug 1087441 v2.1

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https://hg.mozilla.org/integration/gaia-2_1/rev/f664b202baab
Author: Jared Hirsch <ohai@6a68.net>
Desc: backport getJSON method into MockLazyLoader

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https://hg.mozilla.org/integration/gaia-2_1/rev/715dce299ac6
Author: Jared Hirsch <ohai@6a68.net>
Desc: Bug 1087441 (v2.1 backport): Apply font fix to FMD panel header, convert to AMD module. r=arthurcc
Bumping manifests a=b2g-bump