Work around a Numpy deprecation warning

nilmdb/client/numpyclient.py

@@ -25,7 +25,11 @@ def layout_to_dtype(layout):
         atype = '<f' + str(int(ltype[5:]) // 8)
     else:
         raise ValueError("bad layout")
-    return numpy.dtype([('timestamp', '<i8'), ('data', atype, lcount)])
+    if lcount == 1:
+        dtype = [('timestamp', '<i8'), ('data', atype)]
+    else:
+        dtype = [('timestamp', '<i8'), ('data', atype, lcount)]
+    return numpy.dtype(dtype)
 
 class NumpyClient(nilmdb.client.client.Client):
     """Subclass of nilmdb.client.Client that adds additional methods for