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

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https://hg.mozilla.org/integration/gaia-central/rev/8440cdee961d
Author: Yuren Ju <yurenju@gmail.com>
Desc: Merge pull request #18404 from yurenju/migration-folders

Bug 845227 - Remove various app folders like dogfood_apps, showcase_apps... r=@timdream

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https://hg.mozilla.org/integration/gaia-central/rev/269397d3be37
Author: Yuren Ju <yurenju@gmail.com>
Desc: Bug 845227 - Remove various app folders like dogfood_apps, showcase_apps when the app customization is ready
Bumping manifests a=b2g-bump