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

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https://hg.mozilla.org/integration/gaia-central/rev/9960daf91c38
Author: Gareth Aye <gaye@mozilla.com>
Desc: Merge pull request #15077 from gaye/bug-952762

Bug 952762 - Reenable email reply tests

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https://hg.mozilla.org/integration/gaia-central/rev/6eaeb5d63c86
Author: Gareth Aye <gaye@mozilla.com>
Desc: Bug 952762 - Reenable email reply tests