catch NotImplementedError when using isnan in test

old numpy raises this rather than TypeError on inappropriate dtypes

IPython/zmq/tests/test_serialize.py

@@ -87,7 +87,7 b' def _scrub_nan(A):'
         for field in A.dtype.fields.keys():
             try:
                 A[field][numpy.isnan(A[field])] = 0
-            except TypeError:
+            except (TypeError, NotImplementedError):
                 # e.g. str dtype
                 pass