Fix bootstrap cdn url

Author: panesofglass

_layouts/default.html

@@ -12,7 +12,7 @@
     <meta name="msapplication-config" content="{{ 'browserconfig.xml' | absolute_url }}">
     <meta name="msapplication-TileColor" content="#F99D25">
     <meta name="theme-color" content="#F99D25">
-    <link rel="stylesheet" href="//cdn.usebootstrap.com/bootstrap/4.3.1/css/bootstrap.min.css" />
+    <link rel="stylesheet" href="//stackpath.bootstrapcdn.com/bootstrap/4.5.0/css/bootstrap.min.css" />
     <link rel="stylesheet" href="//kit-free.fontawesome.com/releases/latest/css/free.min.css" media="all" />
     <link rel="stylesheet" href="//kit-free.fontawesome.com/releases/latest/css/free-v4-shims.min.css" media="all" />
     <link rel="stylesheet" href="{{ 'Content/style.css' | relative_url }}" />