Fix static class member in URun.

URun.cxx

@@ -9,9 +9,9 @@
 
 ClassImp(URun);
 
-Double_t mProtMass = 0.938272029;
-Double_t mNeutMass = 0.939565360;
-Double_t mPionMass = 0.13957018;
+Double_t URun::mProtMass = 0.938272029;
+Double_t URun::mNeutMass = 0.939565360;
+Double_t URun::mPionMass = 0.13957018;
 
 //----------------
 URun::URun() : TNamed("run", "Run Header" ),