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

========

https://hg.mozilla.org/integration/gaia-central/rev/c9da1e12a2e8
Author: RickyChien <ricky060709@gmail.com>
Desc: Merge pull request #18473 from RickyChien/bug-998759

Bug 998759 - Remove chai.js copying when running make update-common r=@yurenju

========

https://hg.mozilla.org/integration/gaia-central/rev/b0f18968887f
Author: Ricky Chien <ricky060709@gmail.com>
Desc: Bug 998759 - Remove chai.js copying when running make update-common

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "c873d0561b300024c2eadecb18a4fad27441cec6", 
+    "revision": "c9da1e12a2e8b319080cf41acc2ce3d429468d76", 
     "repo_path": "/integration/gaia-central"
 }