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

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https://hg.mozilla.org/integration/gaia-central/rev/8ed6e17eddf3
Author: John Hu <johu@mozilla.com>
Desc: Merge pull request #24685 from huchengtw-moz/bug-1076613

Bug 1076613 - Separate the homescreen related thing from appwindowmanage..., r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/3f72b8913f48
Author: John Hu <im@john.hu>
Desc: Bug 1076613 - Separate the homescreen related thing from appwindowmanager as homescreenwindowmanager
Bumping manifests a=b2g-bump