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

========

https://hg.mozilla.org/integration/gaia-central/rev/efb20ac771e0
Author: Ghislain 'Aus' Lacroix <aus@noiseport.org>
Desc: Merge pull request #33803 from nullaus/bug1189882

Bug 1189882 - Should always switch to root (system app) frame before …

========

https://hg.mozilla.org/integration/gaia-central/rev/efccd3c8375e
Author: Ghislain 'Aus' Lacroix <aus@mozilla.com>
Desc: Bug 1189882 - Should always switch to root (system app) frame before switching to an application. r=mhenretty

b2g/config/gaia.json

@@ -1,9 +1,9 @@
 {
     "git": {
-        "git_revision": "d4212d824001beb182d725f91a07377ee7b1a95d", 
+        "git_revision": "15309984bc5454d8cce463264f0e851e3c7f2d68", 
         "remote": "https://git.mozilla.org/releases/gaia.git", 
         "branch": ""
     }, 
-    "revision": "8971991af400583f3b951ff5230382994f28f46e", 
+    "revision": "efb20ac771e04897cd2a061176ace1af69681bd9", 
     "repo_path": "integration/gaia-central"
 }