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

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https://hg.mozilla.org/integration/gaia-central/rev/ace477ac314e
Author: Amir Nissim <amirnissim@gmail.com>
Desc: Merge pull request #14063 from EverythingMe/937535-collection-bg-header

Bug 937535 - [e.me] Collection header in BG Fullscreen mode is not align...

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https://hg.mozilla.org/integration/gaia-central/rev/531f09f316a5
Author: Amir Nissim <amirnissim@gmail.com>
Desc: Bug 937535 - [e.me] Collection header in BG Fullscreen mode is not aligned [r=evyatron, ranbena]