Bumping gaia.json for 2 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/7cee40cef4a4
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #16414 from KevinGrandon/bug_973941_bg_image_params

Bug 973941 - Background image request follow-up r=amirn

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https://hg.mozilla.org/integration/gaia-central/rev/d10ddb8522e1
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 973941 - Background image request follow-up r=amirn
Bumping manifests a=b2g-bump