Fix Megalinter.

Author: Mattia Faggin

DPG/Tasks/AOTTrack/qaImpPar.cxx

@@ -15,6 +15,8 @@
 /// PID: o2-analysis-pid-tpc-full | o2-analysis-pid-tof-full
 /// Working configuration (2021 Oct 20th): o2-analysis-trackextension -b --aod-file ./AO2D.root | o2-analysis-trackselection -b --isRun3 1 | o2-analysis-pid-tpc-full -b | o2-analysis-pid-tof-full -b | o2-analysis-pp-qa-impact-parameter -b
 
+#include <string>
+
 #include "Framework/AnalysisTask.h"
 #include "Framework/HistogramRegistry.h"
 #include "ReconstructionDataFormats/DCA.h"