doc: Update NOTICE (#39)

diff --git a/NOTICE b/NOTICE
index 66f2232..9de15e3 100644
--- a/NOTICE
+++ b/NOTICE
@@ -1,5 +1,5 @@
 Apache APISIX
-Copyright 2021 The Apache Software Foundation
+Copyright 2021-2022 The Apache Software Foundation
 
 This product includes software developed at
 The Apache Software Foundation (http://www.apache.org/).