Ignore config files of unknown formats.

package.json

@@ -23,7 +23,7 @@
     "url": "git://github.com/vatesfr/xo-server.git"
   },
   "dependencies": {
-    "app-conf": "^0.1.3",
+    "app-conf": "^0.2.0",
     "backoff": "~2.4.0",
     "bluebird": "^2.2.2",
     "chalk": "^0.5.1",

src/main.coffee

@@ -112,7 +112,9 @@ exports = module.exports = $promisify (args) ->
   }
 
   # Loads config files.
-  opts = $wait $appConf.load 'xo-server', opts
+  opts = $wait $appConf.load 'xo-server',
+    defaults: opts
+    ignoreUnknownFormats: true
 
   # Prints a message if deprecated entries are specified.
   for entry in ['users', 'servers']