to_yaml should be to_json

[hopdebee]

Hi Jennifer,

Minor issue.

Thanks for this interesting package !
In the google Colab tutorial (https://colab.research.google.com/drive/14q8-qO93-S4SkIwKJaC5WOSJSEQ8OZYI?usp=sharing) the deepaccess train command fails due to

RuntimeError: Method `model.to_yaml()` has been removed due to security risk of arbitrary code execution. Please use `model.to_json()` instead.

If I change

    def to_yaml(self):
        return self.model.to_yaml()

to

def to_yaml(self):
        return self.model.to_json()

in /train/CNN.py, it works allright.