Atrous Rate illegal for TF Backend

[Benson Tucker]

Hi,

I tried to run this today with Tensorflow as the backend.

Using TF, the atrous rate must be a symmetric tuple (ie, (2, 2)):
https://github.com/usernaamee/keras-wavenet/blob/master/simple-generative-model-regressor.py#L15

[usernaamee]

Thanks for pointing that out, I fixed it now.