Update license year

Author: kazuki43zoo

src/site/xdoc/index.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!--
 
-       Copyright 2018 the original author or authors.
+       Copyright 2018-2019 the original author or authors.
 
        Licensed under the Apache License, Version 2.0 (the "License");
        you may not use this file except in compliance with the License.