Bumping gaia.json for 3 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/a8e0421aa9cc
Author: Dale Harvey <dale@arandomurl.com>
Desc: Bug 1010771 - Check for favicon field. r=me

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https://hg.mozilla.org/integration/gaia-central/rev/9480d9db6420
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #19311 from azasypkin/bug-963013-wrap-into-section

Bug 963013 - [Messages][Refresh] Update bubbles style and layout oft the thread. Date header and message list wrapped into single section element.

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https://hg.mozilla.org/integration/gaia-central/rev/1acd85ed41a2
Author: Aleh Zasypkin <azasypkin@mozilla.com>
Desc: Bug 963013 - [Messages][Refresh] Update bubbles style and layout of the thread. Date header and message list wrapped into single section element. r=julien
Bumping manifests a=b2g-bump