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

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https://hg.mozilla.org/integration/gaia-central/rev/c51da8c9261e
Author: Alive.Kuo <alegnadise@gmail.com>
Desc: Merge pull request #10683 from alivedise/bugzilla/881584_master

Bug 881584 - Stop video activity when visibility is changed. r=djf, a=leo+

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https://hg.mozilla.org/integration/gaia-central/rev/a3692d3da90d
Author: Alive Kuo <alegnadise@gmail.com>
Desc: Bug 881584 - Stop video activity when visibility is changed.