change typo in CrossEntropyLoss (open-mmlab#2534)

The documentation of the use_sigmoid argument in CrossEntropyLoss
currently suggests the sigmoid would be applied in addition to the
softmax function. This change fixes this typo.

Author: jonasitzmann

mmseg/models/losses/cross_entropy_loss.py

@@ -199,7 +199,7 @@ class CrossEntropyLoss(nn.Module):
 
     Args:
         use_sigmoid (bool, optional): Whether the prediction uses sigmoid
-            of softmax. Defaults to False.
+            instead of softmax. Defaults to False.
         use_mask (bool, optional): Whether to use mask cross entropy loss.
             Defaults to False.
         reduction (str, optional): . Defaults to 'mean'.