use new audience url

lib/config.js

@@ -21,7 +21,7 @@ var conf = module.exports = convict({
   },
   audience: {
     doc: "The audience we expect incoming assertions to use",
-    default: "resource://jid1-xidvk7fid7m4aw-at-jetpack"
+    default: "https://firefox.com"
   },
   public_url: {
     format: "url",