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

========

https://hg.mozilla.org/integration/gaia-central/rev/904f39efec16
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Merge pull request #11065 from rexboy7/fixhd-bug895353-master

Bug 895353 - [wallpaper] hdpi/xhdpi resolution assets and layout for Wallpaper app, r=timdream

========

https://hg.mozilla.org/integration/gaia-central/rev/c3afdcf4f6d5
Author: Rex Lee <rexboy@mozilla.com>
Desc: Bug 895353 - [wallpaper] hdpi/xhdpi resolution assets and layout for Wallpaper app

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "aa759fd2b573e6016dc2ba8f05d263a239fc51ae", 
+    "revision": "904f39efec16ef884bac2ff67404c40e5110eb30", 
     "repo_path": "/integration/gaia-central"
 }