Error in Training conv-nets 

Hi, I was using your example code to run the DeepCell. However, I got error in the Training conv-nets .

It seems the error is from: 
```
 from model_zoo import bn_feature_net_61x61 as the_model
 model = the_model(n_channels = 2, n_features = 3, reg = 1e-5)

ValueError: negative dimensions are not allowed
```