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

========

https://hg.mozilla.org/integration/gaia-central/rev/acb6215df962
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Merge pull request #19899 from mschwart/bug991949

Bug 991949 - Cell broadcast ETWS messages show undefined, r=timdream

========

https://hg.mozilla.org/integration/gaia-central/rev/3c8f0d8097aa
Author: Michael Schwartz <mschwart@codeaurora.org>
Desc: Bug 991949 - Cell broadcast ETWS messages show undefined

ETWS messages without a message body use a canned body depending on the
warning type.

Change-Id: I25491fd85894d334bd6a9ab63105379de495ef2a

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "6855ccbf30daba153144eddb84a2aed829e27642", 
+    "revision": "acb6215df962ce143dd3606136d2a6ac6b9783d8", 
     "repo_path": "/integration/gaia-central"
 }