use current host/port

js/slidenotes.js

@@ -3,7 +3,7 @@
   var qs = window.location.href.split('?');
   if (qs.length > 1 && qs[1].match('receiver')) { return; }
 
-  var socket = io.connect('http://localhost:1947');
+  var socket = io.connect(window.location.origin);
 
   Reveal.addEventListener( 'slidechanged', function( event ) {
     var nextindexh;