Bumping gaia.json for 2 gaia-central revision(s)

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https://hg.mozilla.org/integration/gaia-central/rev/4d96cb10a7e4
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #11180 from cctuan/master-898290

Bug 898290 - [Gallery] HD gradient image rename

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https://hg.mozilla.org/integration/gaia-central/rev/c9dbe04b6115
Author: cctuan <georgeiscoming@gmail.com>
Desc: Bug 898290 - [Gallery] HD gradient image rename