Upgrade Font Awesome CDN (yousinix#36)

The Font Awesome CDN has been upgrade to new version.
For example the speaker-deck icon don't show on the actual
version and are ok to show on v5.10.0.

fixes yousinix#31

_includes/head.html

@@ -9,7 +9,7 @@
   <link rel="shortcut icon" type="image/x-icon" href="{{ '/assets/favicon.ico' | relative_url }}">
 
   <!-- Font Awesome CDN -->
-  <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.6.3/css/all.css">
+  <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.10.0/css/all.css">
 
   <!-- Bootstrap CSS CDN -->
   <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css">