add missing module dependency

modules/xmpp/SDPUtil.js

@@ -1,5 +1,5 @@
 /* jshint -W101 */
-var RTCBrowserType = require("../RTC/RTCBrowserType");
+var RTCBrowserType = require('../RTC/RTCBrowserType');
 
 var SDPUtil = {
     filter_special_chars: function (text) {