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

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https://hg.mozilla.org/integration/gaia-central/rev/f5280df8a66c
Author: Mike Habicher <mikeh@mozilla.com>
Desc: Merge pull request #17209 from mikeaich/bug975513_2

Bug 975513 - explicitly add/remove 'devicemotion' event listeners on Camera app focus/blur, r=jdarcangelo

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https://hg.mozilla.org/integration/gaia-central/rev/74a975429d40
Author: Mike Habicher <mikeh@mozilla.com>
Desc: Bug 975513 - explicitly add/remove 'devicemotion' event listeners on Camera app focus/blur
Bumping manifests a=b2g-bump