change tree name in run_at_kfpf.C macro

macro/analysis/common/at_kfpf_interface/run_at_kfpf.C

 void run_at_kfpf(int nEntries               = -1,
                  const std::string& dataset = "test",
-                 const std::string& ATTree  = "aTree") {
+                 const std::string& ATTree  = "rTree") {
   ATKFParticleFinder man;
   const std::string ATFile = dataset + ".analysistree.root";
   man.InitInput(ATFile.c_str(), ATTree.c_str());