[YUNIKORN-617] Update the copyright years in NOTICE file. (#33)

Fixes: #33
diff --git a/release-top-level-artifacts/NOTICE b/release-top-level-artifacts/NOTICE
index d591665..94d7938 100644
--- a/release-top-level-artifacts/NOTICE
+++ b/release-top-level-artifacts/NOTICE
@@ -1,5 +1,5 @@
 Apache YuniKorn (Incubating)
-Copyright 2019-2020 The Apache Software Foundation
+Copyright 2019-2021 The Apache Software Foundation
 
 This product includes software developed at
 The Apache Software Foundation (http://www.apache.org/).