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

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https://hg.mozilla.org/integration/gaia-central/rev/d084b2468675
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #15065 from cctuan/957100

Bug 957100 - [Settings] add marionette for b2g-improve and feedback page

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https://hg.mozilla.org/integration/gaia-central/rev/1b8b7ed503fc
Author: cctuan <georgeiscoming@gmail.com>
Desc: Bug 957100 - [Settings] add marionette for b2g-improve and feedback page