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

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https://hg.mozilla.org/integration/gaia-central/rev/29beb399a2a9
Author: Dominic Kuo <dkuo@mozilla.com>
Desc: Merge pull request #10265 from dominickuo/bug-870320

Bug 870320 - [email] adjust attachments on compose page, r=asutherland

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https://hg.mozilla.org/integration/gaia-central/rev/25ba62b6d988
Author: Dominic Kuo <dkuo@mozilla.com>
Desc: Bug 870320 - [email] adjust attachments on compose page