Bumping gaia.json for 1 gaia-central revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/a9dc5748f9e8
Author: Gabriele Svelto <gsvelto@mozilla.com>
Desc: Bug 911944 - Handle message actions and increase test coverage r=julienw

- Added parsing message actions in SI and SL messages
- Implemented specific behavior for actions such as delete and signal-none
- Fixed a minor issue when doing age-based message replacement
- Added unit-tests for the new functionality
- Added unit-tests coverage to the MessageDB object
- Corrected all jshint linting errors