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

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https://hg.mozilla.org/integration/gaia-central/rev/586fe10680e8
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #17898 from cctuan/991043

Bug 991043 - [Gaia] [Settings] bind _responseHandler to xhr.onreadystate...

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https://hg.mozilla.org/integration/gaia-central/rev/6adab872033c
Author: cctuan <georgeiscoming@gmail.com>
Desc: Bug 991043 - [Gaia] [Settings] bind _responseHandler to xhr.onreadystatechange
Bumping manifests a=b2g-bump