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

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https://hg.mozilla.org/integration/gaia-central/rev/721bbc069f41
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #18467 from KevinGrandon/bug_991261_scroll_to_top

Bug 991261 - [Home2] Method to Return to Top of Vertical Homescreen

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https://hg.mozilla.org/integration/gaia-central/rev/24b48374096f
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 991261 - [Home2] Method to Return to Top of Vertical Homescreen r=me
Bumping manifests a=b2g-bump