Fix internal links

Author: philipbl

Makefile

@@ -10,4 +10,4 @@ build: install
 	bundle exec jekyll build
 
 check_links: build
-	bundle exec htmlproofer --ignore_empty_alt true --ignore_missing_alt true --allow_missing_href=true --ignore-status-codes "0,301,403,999" ./_site
+	bundle exec htmlproofer --ignore_empty_alt true --ignore_missing_alt true --swap-urls "^\/426:" --allow_missing_href=true --ignore-status-codes "0,301,403,999" ./_site