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

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https://hg.mozilla.org/integration/gaia-central/rev/4a5386592d2f
Author: Sebastiaan de Haan <me@sebastiaandehaan.nl>
Desc: Bug 937118 - Bump marionette_client dependency because of bug 937097. r=dhunt