Bumping gaia.json for 1 gaia-central revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/4c72ecffceda
Author: Gabriele Svelto <gsvelto@mozilla.com>
Desc: Bug 934429 - Remove layout/style reflows from the startup path r=rwaldron,julienw

- Do not lazy load CSS files as those trigger a reflow
- Do not read the height of the thread list container when starting up