rstudio: supply missing #include <set>

This was only suceeding by accident, uncovered probably by boost update.
https://hydra.nixos.org/build/228258786/nixlog/4/tail

pkgs/applications/editors/rstudio/default.nix

@@ -148,6 +148,8 @@ in
 
       substituteInPlace src/cpp/session/include/session/SessionConstants.hpp \
         --replace '@pandoc@' ${pandoc}/bin/pandoc
+
+      sed '1i#include <set>' -i src/cpp/core/include/core/Thread.hpp
     '';
 
     hunspellDictionaries = with lib; filter isDerivation (unique (attrValues hunspellDicts));