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

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https://hg.mozilla.org/integration/gaia-central/rev/c864b0ba96d3
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #21242 from KevinGrandon/bug_1030440_vertical_default_layout

Bug 1030440 - [Vertical Homescreen] Optimize default icon configuration

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https://hg.mozilla.org/integration/gaia-central/rev/70f6b31499b8
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1030440 - [Vertical Homescreen] Optimize default icon configuration r=crdlc

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "3d2f77bef0e0622ec6966a76683ff21ec7269eee", 
+    "revision": "c864b0ba96d3145c424b00cf3f6e7a9c624eec96", 
     "repo_path": "/integration/gaia-central"
 }