Implement nodelist in the Doc tag so it may be visited

lib/liquid/tags/doc.rb

@@ -55,6 +55,10 @@ module Liquid
       true
     end
 
+    def nodelist
+      []
+    end
+
     private
 
     def ensure_valid_markup(tag_name, markup, parse_context)

lib/liquid/version.rb

@@ -2,5 +2,5 @@
 # frozen_string_literal: true
 
 module Liquid
-  VERSION = "5.8.0"
+  VERSION = "5.8.1"
 end