NOTICE.txt: update year to 2016
diff --git a/NOTICE.txt b/NOTICE.txt
index 845b696..4c07950 100644
--- a/NOTICE.txt
+++ b/NOTICE.txt
@@ -1,5 +1,5 @@
 Apache HTrace
-Copyright 2015 The Apache Software Foundation
+Copyright 2016 The Apache Software Foundation
 
 This product includes software developed at The Apache Software
 Foundation (http://www.apache.org/).