update paper

      logger.info("Dataset download complete.")

    loader = dc.data.CSVLoader(

        tasks=self.tasks,

        feature_field="reactions",

        featurizer=self.featurizer)

        tasks=self.tasks, feature_field="reactions", featurizer=self.featurizer)

    return loader.create_dataset(dataset_file, shard_size=8192)

  USPTO is a dataset of over 1.8 Million organic chemical reactions extracted

  from US patents and patent applications. The dataset contains the reactions

  in the form of reaction SMILES, which have the general form:

  in the form of reaction SMILES, which have the general format:

  reactant>reagent>product.

  Molnet provides ability to load subsets of the USPTO dataset namely MIT,

         uncertainty-calibrated chemical reaction prediction.

         ACS central science, 5(9), 1572-1583.

  .. [3] Somnath, V. R., Bunne, C., Coley, C. W., Krause, A., & Barzilay, R.

         (2020). Learning Graph Models for Template-Free Retrosynthesis.

         (2020). Learning Graph Models for Retrosynthesis Prediction.

         arXiv preprint arXiv:2006.07038.

  .. [4] Dai, H., Li, C., Coley, C. W., Dai, B., & Song, L. (2020).

         Retrosynthesis prediction with conditional graph logic network.