Change HDF5 setting in Monitor class

libver='earliest' allow for better backward compatibility when switching HDF5 versions.

tracking/monitors/monitors.py

@@ -125,10 +125,10 @@ class Monitor(Element, metaclass=ABCMeta):
                 if len(self._file_storage) == 0:
                     if mpi_mode == True:
                         from mpi4py import MPI
-                        f = hp.File(self.file_name, "w", libver='latest', 
+                        f = hp.File(self.file_name, "w", libver='earliest', 
                              driver='mpio', comm=MPI.COMM_WORLD)
                     else:
-                        f = hp.File(self.file_name, "w", libver='latest')
+                        f = hp.File(self.file_name, "w", libver='earliest')
                     self._file_storage.append(f)
                 else:
                     raise ValueError("File is already open.")