self.group_size*2 should be self.group_size in prepare_data()

[eri24816]

Thank you for providing the code for finetuning the model on custom midi datasets!

I notice that at the line 251 in model.py, the "step" argument of np.arrage is set to self.group_size*2. I think it leads to skipping half of the segments in pairs. Should it be just self.group_size instead of self.group_size*2?

for i in np.arange(0, len(pairs)-self.group_size, self.group_size*2):
    data = pairs[i:i+self.group_size]
        if len(data) == self.group_size:
             segments.append(data)