title: opening old xgboost pickles with the new xgboost version 'XGBClassifier' object has no attribute 'kwargs'
body: <p>I was using xgboost version 0.6 when I pickled some pickle objects.
  Now I upgraded to version 0.82 and when I'm trying to unpickle the old models I get:</p>
  
  <p>AttributeError: 'XGBClassifier' object has no attribute 'kwargs'</p>
  
  <p>I would really like to use these model without re training them, is there any way to open these pickles?</p>