fix broken ref for pygments-css

Author: stevenrick

_includes/head.html

@@ -12,7 +12,7 @@
     <link rel="stylesheet" type="text/css" href="https://fonts.googleapis.com/css?family=Roboto:300,400,500,700|Roboto+Slab:100,300,400,500,700|Material+Icons">
 
     <!-- Code Syntax Highlighting -->
-    <link rel="stylesheet" href="https://gitcdn.link/repo/jwarby/jekyll-pygments-themes/master/{{ site.highlight_theme }}.css" />
+    <link rel="stylesheet" href="https://combinatronics.io/jwarby/pygments-css/master/github.css" />
 
     <!-- Styles -->
     {% if site.icon != empty -%}