Update Font Include for HTTPS

Forgot to use HTTPS on Google Font API

_includes/header.html

@@ -15,7 +15,7 @@
     <link rel="stylesheet" href="{{ site.url }}/assets/dist/app.css">
 
     <!-- Fonts -->
-    <link href='http://fonts.googleapis.com/css?family=Source+Code+Pro' rel='stylesheet' type='text/css' >
+    <link href='https://fonts.googleapis.com/css?family=Source+Code+Pro' rel='stylesheet' type='text/css' >
 
     <!-- Favicon -->
     <link rel="shortcut icon" href="{{ site.url }}/favicon.ico" >