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

Truncated some number of revisions since the previous bump.

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https://hg.mozilla.org/integration/gaia-central/rev/4876e5639f89
Author: Alive.Kuo <alegnadise@gmail.com>
Desc: Merge pull request #10392 from alivedise/bugzilla/883016/gallery-landscape-quality

Bug 883016 - Set default orientation of wallpaper same as homescreen, r=timdream, a=leo+

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https://hg.mozilla.org/integration/gaia-central/rev/4a664294c7ff
Author: Alive Kuo <alegnadise@gmail.com>
Desc: Bug 883016 - Set default orientation of wallpaper same as homescreen

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "3320c4f90ffb0c372f06f7b72d14b54ce0f7a138", 
+    "revision": "4876e5639f89c0a52026aab70b1092293d3d1375", 
     "repo_path": "/integration/gaia-central"
 }