fix include v2

Author: omassen

PWGEM/Dilepton/Core/Dilepton.h

@@ -64,6 +64,7 @@
 #include <Math/Vector4Dfwd.h>
 #include <TH1.h>
 #include <TH2.h>
+#include <TH3.h>
 #include <TList.h>
 #include <TRandom3.h>
 #include <TString.h>