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

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https://hg.mozilla.org/integration/gaia-central/rev/f638a583d026
Author: Wilson Page <wilsonpage@me.com>
Desc: Merge pull request #17894 from wilsonpage/bug/987071

Bug 987071 - [Camera] The screen doesn't going to sleep in the preview gallery

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https://hg.mozilla.org/integration/gaia-central/rev/46b68f91d013
Author: Wilson Page <wilsonpage@me.com>
Desc: Bug 987071 - [Camera] The screen doesn't going to sleep in the preview gallery
Bumping manifests a=b2g-bump