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

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https://hg.mozilla.org/integration/gaia-central/rev/651ff9019404
Author: Ghislain 'Aus' Lacroix <aus@noiseport.org>
Desc: Merge pull request #20674 from nullaus/bug1021857

bug 1021857 - Ensure z-index for AttentionScreen makes it top-most.

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https://hg.mozilla.org/integration/gaia-central/rev/9aa3e71d02f2
Author: Ghislain 'Aus' Lacroix <aus@mozilla.com>
Desc: bug 1021857 - Ensure z-index for AttentionScreen makes it top-most.
Bumping manifests a=b2g-bump