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

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https://hg.mozilla.org/integration/gaia-2_1/rev/49273660f459
Author: Dale Harvey <dale@arandomurl.com>
Desc: Bug 1067573 - Add test to ensure default preloaded top sites show. r=kgrandon
Bumping manifests a=b2g-bump