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

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https://hg.mozilla.org/integration/gaia-central/rev/92e8d5e4f37c
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1021279 - Add a couple more wallpapers to fill the awkward gap in the selection screen r=me
Bumping manifests a=b2g-bump