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

========

https://hg.mozilla.org/integration/gaia-central/rev/154bb18c48ff
Author: Alive.Kuo <alegnadise@gmail.com>
Desc: Merge pull request #12785 from alivedise/bugzilla/908601_master_v2/default-orientation

Bug 908601 - Support default orientation, r=timdream, a=koi+

========

https://hg.mozilla.org/integration/gaia-central/rev/d18785c1ca4c
Author: Alive Kuo <alegnadise@gmail.com>
Desc: Bug 908601 - Support default orientation in system app

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "11e8901eca1c72b15d1461c672666bfd0c3e442d", 
+    "revision": "154bb18c48ff06e41fb7ba24d8f72d520919646f", 
     "repo_path": "/integration/gaia-central"
 }