Fix use of CDN that no longer exists

Author: krlawrence

demos/air-routes-visjs-small.html

@@ -5,8 +5,8 @@
 <meta name='author' content='Kelvin R. Lawrence' />
 <meta name='created' content='2017-Oct-03' />
 <meta name='version' content='0.77' />
-<script type='text/javascript' src='http://visjs.org/dist/vis.js'></script>
-<link href='http://visjs.org/dist/vis.css' rel='stylesheet' type='text/css' />
+<script type='text/javascript' src='http://kelvinlawrence.net/book/vis.js'></script>
+<link href='http://kelvinlawrence.net/book/vis.css' rel='stylesheet' type='text/css' />
 
 <style type='text/css'>
     #mynetwork {