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

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https://hg.mozilla.org/integration/gaia-central/rev/2596fb982d13
Author: Gabriele Svelto <gsvelto@mozilla.com>
Desc: Bug 991666 - Fix removal of old API notifications when selected from the toaster r=alive
Bumping manifests a=b2g-bump