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

========

https://hg.mozilla.org/integration/gaia-central/rev/a9dab91a7f8c
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #18767 from gasolin/issue-973445

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

========

https://hg.mozilla.org/integration/gaia-central/rev/d47b809fda5a
Author: gasolin <gasolin@gmail.com>
Desc: Bug 973445 - [settings] refactor Sound panel with AMD pattern
- remove fowardlock shim
Bumping manifests a=b2g-bump