Merge pull request #128 from Ynzl/fix-build-metric

fix bug: pass **kwargs when building metric with string

inferno/trainers/basic.py

@@ -516,7 +516,7 @@ def build_metric(self, method, **kwargs):
         elif isinstance(method, str):
             assert hasattr(metrics, method), \
                 "Could not find the metric '{}'.".format(method)
-            self._metric = getattr(metrics, method)()
+            self._metric = getattr(metrics, method)(**kwargs)
         else:
             raise NotImplementedError
         return self