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

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https://hg.mozilla.org/integration/gaia-central/rev/c841634cb485
Author: Dale Harvey <dale@arandomurl.com>
Desc: Bug 898326 - Disable buttons when switching camera. r=djf

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https://hg.mozilla.org/integration/gaia-central/rev/e71e50ddfde5
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Bug 890427: use camera API's onPreviewStateChange callback to avoid deadlock. r=johu

do the same thing in loadCameraPreview