added string library in std

Author: Sawan Sawan

PWGLF/Tasks/Resonances/higherMassResonances.cxx

@@ -51,6 +51,7 @@
 #include <array>
 #include <cmath>
 #include <cstdlib>
+#include <string>
 #include <vector>
 
 using namespace o2;