change error code

Author: wjlei1990

pytomo3d/utils/download.py

@@ -113,7 +113,7 @@ def download_stationxml(stations, starttime, endtime, outputdir=".",
         except Exception as e:
             print("Failed to download StationXML '%s' due to: %s"
                   % (station_id, str(e)))
-            error_code = 1
+            error_code = 2
         _status[station_id] = error_code
 
     return _status