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

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https://hg.mozilla.org/integration/gaia-central/rev/4018738e7884
Author: Gabriele Svelto <gsvelto@mozilla.com>
Desc: Bug 980854 - Remove the workarounds for glitchy touch tones now that bug 848954 has landed r=Rik
Bumping manifests a=b2g-bump