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

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https://hg.mozilla.org/integration/gaia-central/rev/8ac14d4784ef
Author: lissyx <lissyx+github@lissyx.dyndns.org>
Desc: Merge pull request #15802 from jankeromnes/layers

Bug 960933 - Show app debug information in a devtools overlay. r=vingtetun

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https://hg.mozilla.org/integration/gaia-central/rev/abdacf3e7778
Author: Jan Keromnes <janx@linux.com>
Desc: Bug 960933 - Show app debug information in a devtools overlay. r=vingtetun
Bumping manifests a=b2g-bump