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

========

https://hg.mozilla.org/integration/gaia-central/rev/a9a3ec28034b
Author: Evelyn Eastmond <evhan55@gmail.com>
Desc: Bug 959196 - [Messages][Drafts] Don't auto-save new draft when hiding app and then draft is discarded r=rwaldron

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "8028f7c930fd784254885cb4477cb6bf3513e44d", 
+    "revision": "a9a3ec28034be1d4324aebbfb52827dafc975765", 
     "repo_path": "/integration/gaia-central"
 }