Add missing include statement to fix compiler error

analysis/PWGC2F/femtoscopy/nicafemto/format/unigen/NicaUnigenSource.cxx

@@ -13,6 +13,7 @@
 #include "UParticle.h"
 #include <TBranch.h>
 #include <fstream>
+#include <iostream>
 
 NicaUnigenSource::NicaUnigenSource()
   : fUnigenChain(NULL), fFileName("data.root"), fEvent(NULL) {}