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

========

https://hg.mozilla.org/integration/gaia-central/rev/4b9afd5e0f3e
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1010640 - [Home2] Follow-up, fix shadow x offset
Bumping manifests a=b2g-bump