Update copyright date

JIRA: MADLIB-1466

The rat check test failed because our copyright year was not updated.

Co-authored-by: Ekta Khanna <ekhanna@vmware.com>
diff --git a/NOTICE b/NOTICE
index 10b9387..b59ed0f 100644
--- a/NOTICE
+++ b/NOTICE
@@ -1,5 +1,5 @@
 Apache MADlib
-Copyright 2016-2020 The Apache Software Foundation.
+Copyright 2016-2021 The Apache Software Foundation.
 
 This product includes software developed at
 The Apache Software Foundation (http://www.apache.org/).