no key in meta.data called 'class proportions'

[ritikasaboo13]

In the data.py file, the class_weights() function calculates class weights based on the key 'class proportions' but this key does not exist. The correct key is 'class_ratio' / 'class ratio'.

I am happy to make this correction, although I am not sure where the function is being used during training and perhaps the function is redundant.