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

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https://hg.mozilla.org/integration/gaia-central/rev/57ac935d11ae
Author: Arthur Chen <crh0716@gmail.com>
Desc: Merge pull request #16477 from crh0716/974253

Bug 974253 - Set preferred network type on startup based on the user preference r=jaoo

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https://hg.mozilla.org/integration/gaia-central/rev/9929c37e9bc5
Author: Arthur Chen <crh0716@gmail.com>
Desc: Bug 974253 - Set preferred network type on startup based on the user preference
Bumping manifests a=b2g-bump