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

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https://hg.mozilla.org/integration/gaia-central/rev/208aeea53c36
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #21001 from sfoster/bug-1023863-dividers

Bug 1023863 - Adjust divider margins

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https://hg.mozilla.org/integration/gaia-central/rev/2cec54f07efe
Author: Sam Foster <sfoster@mozilla.com>
Desc: Bug 1023863 - Adjust divider margins and grid item heights. r=kgrandon
Bumping manifests a=b2g-bump