Bumping gaia.json for 1 gaia-central revision(s) a=gaia-bump

========

https://hg.mozilla.org/integration/gaia-central/rev/ab822e8ed326
Author: Corey Frang <gnarf37@gmail.com>
Desc: Bug 936643 - [Settings] Implement ListView.destroy() - r=arthurcc

- Adds `Observable().unobserve` as well as `ObservableArray.unobserve()`
- Adds `ListView().destroy()`
- Adds an element cache for `ListView` so that a re-used element can automatically destroy it's old `ListView`

Closes gh-13724

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "b7b700d7389880370c8aa2dc77973ad8c1bd7ca8", 
+    "revision": "ab822e8ed3266245022eee83beacf679727a507e", 
     "repo_path": "/integration/gaia-central"
 }