docs: adjust to Hugo 0.128.0

coming with changes to extension handling

Author: McShelby

exampleSite/config/_default/hugo.toml

@@ -68,9 +68,12 @@ summaryLength = 10
     renderer.unsafe = true
 
   [markup.goldmark.extensions]
+    strikethrough = false
 
     # use Markdown extensions for this showcase
     [markup.goldmark.extensions.extras]
+      [markup.goldmark.extensions.extras.delete]
+        enable = true
       [markup.goldmark.extensions.extras.insert]
         enable = true
       [markup.goldmark.extensions.extras.mark]