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

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https://hg.mozilla.org/integration/gaia-central/rev/9d7bb621e714
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #17938 from gasolin/issue-973445

Bug 973445 - [settings] refactor Sound panel with AMD pattern, r=arthur

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https://hg.mozilla.org/integration/gaia-central/rev/d89211fbcd69
Author: gasolin <gasolin@gmail.com>
Desc: Bug 973445 - [settings] refactor Sound panel with AMD pattern

- add tone tests
Bumping manifests a=b2g-bump