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

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https://hg.mozilla.org/integration/gaia-central/rev/1b6e18072e79
Author: Francisco Jordano <arcturus@ardeenelinfierno.com>
Desc: Merge pull request #12686 from KevinGrandon/bug_923873_contacts_defer_overlay

Bug 923873 - [Contacts] Do not load overlay.js for list display

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https://hg.mozilla.org/integration/gaia-central/rev/64a0b968dcbd
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 923873 - [Contacts] Do not load overlay.js for list display