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

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https://hg.mozilla.org/integration/gaia-central/rev/f76db748e12b
Author: Anthony Ricaud <anthony@ricaud.me>
Desc: Merge pull request #11853 from Rik/attention-screen-size-908186

Bug 908186 - Listen to mozbrowserresize events to hide or show the atten... r=etienne

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https://hg.mozilla.org/integration/gaia-central/rev/564bd1d934b1
Author: Anthony Ricaud <anthony@ricaud.me>
Desc: Bug 908186 - Listen to mozbrowserresize events to hide or show the attention screen