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

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https://hg.mozilla.org/integration/gaia-central/rev/5bf674ca0f8e
Author: dwi2 <dwi2@dwi2.com>
Desc: Merge pull request #15003 from dwi2/bug956193

Disable 'layers.composer2d.enabled' (checkbox 'Enable hardware composer'...

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https://hg.mozilla.org/integration/gaia-central/rev/0cba7cd1987f
Author: tzhuang <tzhuang@mozilla.com>
Desc: Disable 'layers.composer2d.enabled' (checkbox 'Enable hardware composer' in Settings app) on flatfish