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

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https://hg.mozilla.org/integration/gaia-central/rev/966752354a41
Author: James Lal <james@lightsofapollo.com>
Desc: Merge pull request #10899 from julienw/891927-fixes-sinon-implementation

Bug 891927 - [test-agent] the sinon sandbox is not always restored when ...

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https://hg.mozilla.org/integration/gaia-central/rev/b4a0ad8bb616
Author: Julien Wajsberg <felash@gmail.com>
Desc: Bug 891927 - [test-agent] the sinon sandbox is not always restored when it's used in the most outer suite's setup r=jlal