RATIS-875. Bump the copyright year in the NOTICE of thirdparty

(cherry picked from commit 7a6b023e4154cfbec7fe07f28f796fd10847a119)
diff --git a/NOTICE b/NOTICE
index a417abb..08e98d7 100644
--- a/NOTICE
+++ b/NOTICE
@@ -1,3 +1,3 @@
 Apache Ratis Thirdparty
 
-Copyright 2018 The Apache Software Foundation
+Copyright 2020 The Apache Software Foundation