Fix dns links in head

Author: cotes2020

_includes/head.html

@@ -51,8 +51,8 @@
   {% endif %}
 
   <!-- jsDelivr CDN -->
-  <link rel="preconnect" href="cdn.jsdelivr.net">
-  <link rel="dns-prefetch" href="cdn.jsdelivr.net">
+  <link rel="preconnect" href="https://cdn.jsdelivr.net">
+  <link rel="dns-prefetch" href="https://cdn.jsdelivr.net">
 
   <!-- Bootstrap -->
   <link rel="stylesheet"