Fix loss metric.

combo/models/model.py

@@ -53,7 +53,7 @@ class NERModel(heads.Head):
         )
 
         if tags is not None:
-            self._loss = output["loss"]
+            self._loss = output["loss"].cpu().item()
             self._accuracy_metric(output["probability"], tags, word_mask)
             self._f1_metric(output["probability"], tags, word_mask)