Allow note html to be regenerated from markdown

app/services/issuable/clone/content_rewriter.rb

@@ -28,6 +28,7 @@ module Issuable
           new_params = {
             project: new_entity.project, noteable: new_entity,
             note: rewrite_content(new_note.note),
+            note_html: nil,
             created_at: note.created_at,
             updated_at: note.updated_at
           }