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

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https://hg.mozilla.org/integration/gaia-central/rev/c7a34ae95f67
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Merge pull request #16667 from pivanov/bug-949024

Bug 949024 - Update Branded Wallpapers Sizes for v.1.4

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https://hg.mozilla.org/integration/gaia-central/rev/11cfc3fcb2a0
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Bug 949024 - Update Branded Wallpapers Sizes for v.1.4
Bumping manifests a=b2g-bump