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

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https://hg.mozilla.org/integration/gaia-central/rev/af1c2fdc3e4b
Author: Dominic Kuo <dkuo@mozilla.com>
Desc: Merge pull request #18484 from dominickuo/bug-910055

Bug 910055 - [Settings] add media slider to the sound region, r=crh0716

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https://hg.mozilla.org/integration/gaia-central/rev/a33bf018f9ff
Author: Dominic Kuo <dkuo@mozilla.com>
Desc: Bug 910055 - [Settings] add media slider to the sound region
Bumping manifests a=b2g-bump