Fix training Conditional Random Fields on GPU (allenai#5313)

allennlp/modules/conditional_random_field.py

@@ -323,7 +323,7 @@ def forward(
         """
 
         if mask is None:
-            mask = torch.ones(*tags.size(), dtype=torch.bool)
+            mask = torch.ones(*tags.size(), dtype=torch.bool, device=inputs.device)
         else:
             # The code below fails in weird ways if this isn't a bool tensor, so we make sure.
             mask = mask.to(torch.bool)