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

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https://hg.mozilla.org/integration/gaia-central/rev/cc720fef4c09
Author: Arthur Chen <crh0716@gmail.com>
Desc: Merge pull request #12460 from crh0716/919861

Bug 919861 - Connect a new device until the previous one is disconnected r=evelyn

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https://hg.mozilla.org/integration/gaia-central/rev/b0f63b4e4285
Author: Arthur Chen <crh0716@gmail.com>
Desc: Bug 919861 - Connect a new device until the previous one is disconnected