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

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https://hg.mozilla.org/integration/gaia-central/rev/846f8e708936
Author: Gareth Aye <gaye@mozilla.com>
Desc: Merge pull request #10983 from gaye/bug-889396

Bug 889396 - Sync button went away r=lightsofapollo

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https://hg.mozilla.org/integration/gaia-central/rev/87f21415dc13
Author: gaye <gaye@mozilla.com>
Desc: Bug 889396 - Sync button went away