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

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https://hg.mozilla.org/integration/gaia-central/rev/9f4db6bcede8
Author: John Hu <johu@mozilla.com>
Desc: Merge pull request #25247 from huchengtw-moz/bug-1074040-fork-add-landing-app

Bug 1074040 fork add landing app, r=alive, evelyn

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https://hg.mozilla.org/integration/gaia-central/rev/b2b4f88b02dd
Author: John Hu <johu@mozilla.com>
Desc: Bug 1074040 - [Stingray] fork system, remove useless modules and add support of landing app

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "eb3cd285b797bec69311da50abe0f74293f12938", 
+    "revision": "9f4db6bcede8557cb8ac746fc977bc50bff2278b", 
     "repo_path": "/integration/gaia-central"
 }