Fix typo in previous commit

geomagio/TimeseriesUtility.py

@@ -225,7 +225,7 @@ def merge_streams(*streams):
             # 1 = when there is overlap, use data from trace with last endtime
             method=1,
             # np.nan = work-around for (problematic) intermediate masked arrays
-            filled_value=numpy.nan)
+            fill_value=numpy.nan)
 
     # convert back to NaN filled array
     merged = unmask_stream(split)