Replace deprecated numpy.fromstring usage

nilmdb/client/numpyclient.py

@@ -59,7 +59,7 @@ class NumpyClient(nilmdb.client.client.Client):
         dtype = self._get_dtype(path, layout)
 
         def to_numpy(data):
-            a = numpy.fromstring(data, dtype)
+            a = numpy.frombuffer(data, dtype)
             if structured:
                 return a
             return numpy.c_[a['timestamp'], a['data']]