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

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https://hg.mozilla.org/integration/gaia-central/rev/3539f47a7dcf
Author: Ben Francis <ben@tola.me.uk>
Desc: Bug 963173 - Ensure address bar is always displayed when a different tab is selected. r=daleharvey
Bumping manifests a=b2g-bump