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

========

https://hg.mozilla.org/integration/gaia-central/rev/15fe9d38266b
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #13684 from gasolin/issue-936395

Bug 936395 - [Notification] Notification counter doesn't work correctly, r=alive

========

https://hg.mozilla.org/integration/gaia-central/rev/cc1c7a3aba63
Author: gasolin <gasolin@gmail.com>
Desc: Bug 936395 - [Notification] Notification counter doesn't work correctly

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "ab822e8ed3266245022eee83beacf679727a507e", 
+    "revision": "15fe9d38266bf2aac0d82e4dae5659684e8aaa41", 
     "repo_path": "/integration/gaia-central"
 }