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

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https://hg.mozilla.org/integration/gaia-central/rev/9b4d3f14208d
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #17495 from gasolin/sheriff976986

Merge pull request #16947 from dwi2/bug976986, r=timdream

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https://hg.mozilla.org/integration/gaia-central/rev/61d7ab0cfc79
Author: dwi2 <dwi2@dwi2.com>
Desc: Merge pull request #16947 from dwi2/bug976986

Bug 976986 - SettingsListener should have unobserve() method

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "branch": "", 
         "revision": ""
     }, 
-    "revision": "9ee041e12d23cc99e94dca49b0219e7d101d1e5a", 
+    "revision": "9b4d3f14208d403ded9728102bd617044d3a5ba6", 
     "repo_path": "/integration/gaia-central"
 }