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

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https://hg.mozilla.org/integration/gaia-central/rev/312d5c0596e5
Author: Ben Kelly <bkelly@mozilla.com>
Desc: Merge pull request #12832 from wanderview/email-remove-onclick

Bug 926524: Remove bound click handler in MessageListTopbar.  r=gaye

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https://hg.mozilla.org/integration/gaia-central/rev/b8c548bd56e9
Author: Ben Kelly <ben@wanderview.com>
Desc: Bug 926524: Remove bound click handler in MessageListTopbar.