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

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https://hg.mozilla.org/integration/gaia-central/rev/761b205f4e8b
Author: Eitan Isaacson <eitan@monotonous.org>
Desc: Merge pull request #16676 from eeejay/bug-967832

Bug 967832 - [Homescreen] Set fake-icon to aria-hidden. r=21

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https://hg.mozilla.org/integration/gaia-central/rev/a17d460301f0
Author: Eitan Isaacson <eitan@monotonous.org>
Desc: Bug 967832 - [Homescreen] Set fake-icon to aria-hidden.
Bumping manifests a=b2g-bump