Add missing LinkDef for Tracklet64 class

Author: martenole

DataFormats/Detectors/TRD/src/DataFormatsTRDLinkDef.h

@@ -21,6 +21,7 @@
 #pragma link C++ struct o2::trd::TrackletMCMHeader + ;
 #pragma link C++ struct o2::trd::TrackletMCMData + ;
 #pragma link C++ class o2::trd::Tracklet64 + ;
+#pragma link C++ class std::vector < o2::trd::Tracklet64> + ;
 #pragma link C++ class std::vector < o2::trd::TriggerRecord > +;
 #pragma link C++ class std::vector < o2::trd::LinkRecord > +;