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

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https://hg.mozilla.org/integration/gaia-central/rev/6cf91c6fcd3c
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #12016 from gasolin/issue-911668

Bug 911668 - [homescreen] change build-in apps orientation to default, r=timdream

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https://hg.mozilla.org/integration/gaia-central/rev/76a003c7bb0e
Author: gasolin <gasolin@gmail.com>
Desc: Bug 911668 - [homescreen] change build-in apps orientation to default