Bumping gaia.json for 2 gaia-central revision(s)

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https://hg.mozilla.org/integration/gaia-central/rev/85817f79d7d6
Author: Ian Liu <iliu@mozilla.com>
Desc: Merge pull request #10782 from ian-liu/clock/Bug881139_hdpi/xhdpi_resolution_assets_and_layout_for_Clock_app

Bug 881139 - hdpi/xhdpi resolution assets and layout for Clock app, r=@rexboy7

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https://hg.mozilla.org/integration/gaia-central/rev/18c207cee4e4
Author: ian-liu <iliu@mozilla.com>
Desc: Bug 881139 - hdpi/xhdpi resolution assets and layout for Clock app

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "b1f9cd3cbbb1478fc2cb31ecb823fd11634cbf19", 
+    "revision": "85817f79d7d68a3a46a74ec6866b7b3c4081b1ac", 
     "repo_path": "/integration/gaia-central"
 }