try to avoid copying also when fitting scaler

toolkit.py

@@ -19,6 +19,7 @@ import csv
 import math
 import glob
 import shutil
+import gc
 
 import logging
 logger = logging.getLogger("KerasROOTClassification")
@@ -536,7 +537,10 @@ class ClassificationProject(object):
                 else:
                     raise ValueError("Scaler type {} unknown".format(self.scaler_type))
                 logger.info("Fitting {} to training data".format(self.scaler_type))
+                orig_copy_setting = self.scaler.copy
+                self.scaler.copy = False
                 self._scaler.fit(self.x_train, **scaler_fit_kwargs)
+                self.scaler.copy = orig_copy_setting
                 joblib.dump(self._scaler, filename)
         return self._scaler