Set copyright year to 2020

stager_access.py

 #! /usr/bin/env python3
 
-# Copyright 2019 Stichting Nederlandse Wetenschappelijk Onderzoek Instituten,
+# Copyright 2020 Stichting Nederlandse Wetenschappelijk Onderzoek Instituten,
 # ASTRON Netherlands Institute for Radio Astronomy
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.