Update the year in the NOTICE file to 2021

NOTICE

diff --git a/NOTICE b/NOTICE
index 8a60ef5..e09832b 100644
--- a/NOTICE
+++ b/NOTICE
@@ -1,5 +1,5 @@
 Apache NetBeans
-Copyright 2017-2020 The Apache Software Foundation
+Copyright 2017-2021 The Apache Software Foundation
 
 This product includes software developed at
 The Apache Software Foundation (http://www.apache.org/).

nbbuild/notice-stub.txt

diff --git a/nbbuild/notice-stub.txt b/nbbuild/notice-stub.txt
index e6c1723..e0ce5df 100644
--- a/nbbuild/notice-stub.txt
+++ b/nbbuild/notice-stub.txt
@@ -1,5 +1,5 @@
 Apache NetBeans
-Copyright 2017-2020 The Apache Software Foundation
+Copyright 2017-2021 The Apache Software Foundation
 
 This product includes software developed at
 The Apache Software Foundation (http://www.apache.org/).