XGBoost model serializaiton message #407

 !> se <- bambu(reads = "cell1_sort.bam",
 +             annotations = annotation,
 +             genome = Hsapiens)
 --- Start generating read class files ---
 [20:58:14] WARNING: src/learner.cc:553:
   If you are loading a serialized model (like pickle in Python, RDS in R) generated by
   older XGBoost, please export the model by calling `Booster.save_model` from that version
   first, then load it back in current version. See:

     https://xgboost.readthedocs.io/en/latest/tutorials/saving_model.html

   for more details about differences between saving model and serializing.
...