utils.py: compatibility with new pytorch

utils.py

@@ -6,7 +6,7 @@ import torch
 def get_mask_from_lengths(lengths):
     max_len = torch.max(lengths).item()
     ids = torch.arange(0, max_len, out=torch.cuda.LongTensor(max_len))
-    mask = (ids < lengths.unsqueeze(1)).byte()
+    mask = (ids < lengths.unsqueeze(1)).bool()
     return mask