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

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https://hg.mozilla.org/integration/gaia-central/rev/7eb40483a84b
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #19914 from gasolin/issue-938467

Bug 938467 - gUM permission grant scenario - remember my choice support, r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/c84271befd85
Author: gasolin <gasolin@gmail.com>
Desc: Bug 938467 - gUM permission grant scenario - remember my choice support
- add permissions in settings
- replace remember my choice from switch to checkbox
- UX polish
- make permission dialog content scrollable when exceed max size in landscape
Bumping manifests a=b2g-bump