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

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https://hg.mozilla.org/integration/gaia-central/rev/d56d845a52e0
Author: Jared Hirsch <ohai@6a68.net>
Desc: Merge pull request #18392 from 6a68/resubmit-bug-987418-fxa-system-app-copy

Resubmit bug 987418 fxa system app copy

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https://hg.mozilla.org/integration/gaia-central/rev/8a45ffad3d7d
Author: Jared Hirsch <ohai@6a68.net>
Desc: Bug 987418 - FxA System app copy/l10n changes, resubmitted. r=ferjm
Bumping manifests a=b2g-bump