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

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https://hg.mozilla.org/integration/gaia-central/rev/934fbbe46bdb
Author: Gabriele Svelto <gsvelto@mozilla.com>
Desc: Bug 978553 - Don't try to insert the message body if the activity didn't populate it r=julienw
Bumping manifests a=b2g-bump