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

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https://hg.mozilla.org/integration/gaia-central/rev/470c81220a0a
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #13052 from denehs/bug928821

Bug 928821 - B2G MMS: put deliveryStatus[] into a more generic structure...

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https://hg.mozilla.org/integration/gaia-central/rev/342bbe4dd3c4
Author: Shao Hang Kao <denehs@gmail.com>
Desc: Bug 928821 - B2G MMS: put deliveryStatus[] into a more generic structure MmsDeliveryInfo[]