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

========

https://hg.mozilla.org/integration/gaia-central/rev/55fbd5145bbd
Author: Dave Hunt <dave.hunt@gmail.com>
Desc: Bug 949459 - Restore support for older branches in gaia_apps.js. r=akuo

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "956a9d7e094c944d585b1896dc5bc5943b69c632", 
+    "revision": "55fbd5145bbdcfd23ff702819f7a556adad830f4", 
     "repo_path": "/integration/gaia-central"
 }