Update index.html

Author: riverfor

docs/index.html

@@ -5,7 +5,7 @@
     <title>QPython - Course</title>
     <meta charset="utf-8">
     <meta name="viewport" content="width=device-width, initial-scale=1,maximum-scale=1, user-scalable=no">
-    <link href="//cdn.bootcss.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet">
+<link href="//maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet">
     <script src="//cdn.bootcss.com/jquery/3.2.1/jquery.min.js"></script>
     <link rel="stylesheet" type="text/css" href="//www.qpython.org/static/qpython_theme.css">
     <link rel="stylesheet" type="text/css" href="static/course_web.css">
@@ -234,4 +234,4 @@
     ga('create', 'UA-103260045-3', 'auto');
     ga('send', 'pageview');
 
-</script>
+</script>