Update markup engine config

Explicitly set the markup engine as blackfriday so the site renders with the current version of hugo.

config.toml

@@ -31,6 +31,9 @@ pygmentsStyle = "tango"
 [permalinks]
 blog = "/:section/:year/:month/:day/:slug/"
 
+[markup]
+defaultMarkdownHandler = "blackfriday"
+
 ## Configuration for BlackFriday markdown parser: https://github.com/russross/blackfriday
 [blackfriday]
 plainIDAnchors = true