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

========

https://hg.mozilla.org/integration/gaia-central/rev/20869b028aab
Author: Rex KM Lee <rexboy@mozilla.com>
Desc: Merge pull request #10855 from rexboy7/fixhd-881143-dialer-master

Bug 881143 - [HD][Dialer] hdpi/xhdpi resolution assets and layout for Dialer app. r=gtorodelvalle

========

https://hg.mozilla.org/integration/gaia-central/rev/92424a531110
Author: Rex Lee <rexboy@mozilla.com>
Desc: Bug 881143 - [HD][Dialer] hdpi/xhdpi resolution assets and layout for Dialer app

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "287688e19d1a0ded303c4edd1e9bfb945cbd7fdf", 
+    "revision": "20869b028aab74ab04131c4e2e76fadf91b57404", 
     "repo_path": "/integration/gaia-central"
 }