update year to 2021 (#85)

diff --git a/NOTICE b/NOTICE
index e646f51..2ca1b04 100644
--- a/NOTICE
+++ b/NOTICE
@@ -1,5 +1,5 @@
 Apache SkyWalking
-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/).
diff --git a/dist/NOTICE b/dist/NOTICE
index 5b69da2..870d20b 100644
--- a/dist/NOTICE
+++ b/dist/NOTICE
@@ -1,5 +1,5 @@
 Apache SkyWalking
-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/).