Add support for li attribute to li element

app/lib/sanitize_config.rb

@@ -91,6 +91,7 @@ class Sanitize
         'abbr'       => %w(title),
         'blockquote' => %w(cite),
         'ol'         => %w(start reversed),
+        'li'         => %w(value),
       },
 
       add_attributes: {