fix typo in mask_decoder.py

tranformer -> transformer

segment_anything/modeling/mask_decoder.py

@@ -26,7 +26,7 @@ class MaskDecoder(nn.Module):
     ) -> None:
         """
         Predicts masks given an image and prompt embeddings, using a
-        tranformer architecture.
+        transformer architecture.
 
         Arguments:
           transformer_dim (int): the channel dimension of the transformer