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

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https://hg.mozilla.org/integration/gaia-central/rev/281ec6617899
Author: Alive.Kuo <alegnadise@gmail.com>
Desc: Merge pull request #11894 from alivedise/bugzilla/802643/remove-workaround-in-email-app

Bug 802643 - Remove activity workaround in email app, r=asuth

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https://hg.mozilla.org/integration/gaia-central/rev/b511541d6283
Author: Alive Kuo <alegnadise@gmail.com>
Desc: Bug 802643 - Remove activity workaround in email app