forgot to require plugins

src/socket.io/topics.js

@@ -7,6 +7,7 @@ var nconf = require('nconf'),
 	topics = require('../topics'),
 	categories = require('../categories'),
 	privileges = require('../privileges'),
+	plugins = require('../plugins'),
 	notifications = require('../notifications'),
 	threadTools = require('../threadTools'),
 	websockets = require('./index'),