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

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https://hg.mozilla.org/integration/gaia-central/rev/591c866cb04a
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #21995 from KevinGrandon/bug_1041607_async_xhr_in_tests

Bug 1041607 - Remove synchronous XHR from tests

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https://hg.mozilla.org/integration/gaia-central/rev/f0666d464d19
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1041607 - Remove synchronous XHR from tests r=amirn
Bumping manifests a=b2g-bump