Add back in commented out class

Author: Dr15Jones

DataFormats/StdDictionaries/src/classes_def_others.xml

@@ -25,5 +25,5 @@
  <class name="std::set<std::basic_string<char> >"/>
  <class name="std::atomic<int>"/>
  <class name="std::__atomic_base<int>"/>
-<!-- <class name="std::monostate"/>-->
+<class name="std::monostate"/>
 </lcgdict>