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

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https://hg.mozilla.org/integration/gaia-central/rev/b8ef6bf859d7
Author: John Hu <johu@mozilla.com>
Desc: Merge pull request #12884 from huchengtw-moz/camera/Bug_904484_use_device_motion_version2

Bug 904484 - [Camera] Camera app can not calculate the orientation if th... r=djf

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https://hg.mozilla.org/integration/gaia-central/rev/f17ff748a36f
Author: John Hu <johu@mozilla.com>
Desc: Bug 904484 - [Camera] Camera app can not calculate the orientation if there's no orientation sensor