; for Bidirectional GRU with pretrained word vectors
                      - &#39;bert&#39; for BERT Text Classification
                      - &#39;distilbert&#39; for Hugging Face DistilBert model

        train_data (tuple): a tuple of numpy.ndarrays: (x_train, y_train)
        preproc: a ktrain.text.TextPreprocessor instance.
                 As of v0.8.0, this is required.
        metrics(list): metrics to use
        verbose (boolean): verbosity of output
    Return:
        model (Model): A Keras Mo