Update dice.py

The dice loss varies with batch sizes, and this issue remains unresolved.
#712 (comment)

Author: nistring

segmentation_models_pytorch/losses/dice.py

@@ -70,7 +70,7 @@ def forward(self, y_pred: torch.Tensor, y_true: torch.Tensor) -> torch.Tensor:
 
         bs = y_true.size(0)
         num_classes = y_pred.size(1)
-        dims = (0, 2)
+        dims = (2)
 
         if self.mode == BINARY_MODE:
             y_true = y_true.view(bs, 1, -1)