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

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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

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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

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "f5f91029153863981bcee3226734d3039bfe2ffa", 
+    "revision": "a9dab91a7f8c689318d6b995c71d4a811ce7e0ef", 
     "repo_path": "/integration/gaia-central"
 }