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

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https://hg.mozilla.org/integration/gaia-central/rev/6ec8b59d9a58
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #16071 from flodolo/bug968071_mediainfo

Bug 968071 - Taken/Shoot date in image/video info not localizable

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https://hg.mozilla.org/integration/gaia-central/rev/ca23d6f37535
Author: Francesco Lodolo (:flod) <flod@lodolo.net>
Desc: Bug 968071 - Taken/Shoot date in image/video info not localizable

This approach let us reuse an existing string, so it can be ported to
1.3

Note that this also changes the en-US format from mm-dd-YYYY to
mm/dd/YYYY
Bumping manifests a=b2g-bump