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

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https://hg.mozilla.org/integration/gaia-central/rev/bdd742865bf6
Author: Julien Wajsberg <felash@gmail.com>
Desc: Merge pull request #13793 from julienw/add-expiration-and-conditional-content-logic-in-httpd-js

Bug 939729 - With httpd.js we sometimes don't get the most recent versio...

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https://hg.mozilla.org/integration/gaia-central/rev/d0ec3153d0b2
Author: Julien Wajsberg <felash@gmail.com>
Desc: Bug 939729 - With httpd.js we sometimes don't get the most recent version of the file r=vingtetun

This patch:
* makes all files expire immediately, forcing a revalidation by Firefox
* implements conditional requests with Last-Modified-Since