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

========

https://hg.mozilla.org/integration/gaia-central/rev/3b558b81bc51
Author: Alive.Kuo <alegnadise@gmail.com>
Desc: Merge pull request #10152 from leob2g/Bug_878662_Sound_Manager_CEWarningDialog_is_displayed_at_CEWarningVol_+_1

Bug 878662 - [System][Sound Manager] CEWarningDialog is displayed in incorrect timing, r=alive

========

https://hg.mozilla.org/integration/gaia-central/rev/415ee260023a
Author: hanj.kim <hanj.kim@lge.com>
Desc: Bug 878662 - [System][Sound Manager] CEWarningDialog is displayed at CEWarningVol + 1

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "f5f12069851f39b356d9ae276bdd5f17bf44357c", 
+    "revision": "3b558b81bc51aeb3034c27c498554c8eda352bb0", 
     "repo_path": "/integration/gaia-central"
 }