[MINOR] Update copyright year in the footer

Author: j143

_src/_includes/themes/apache/partials/_footer.html

@@ -22,8 +22,10 @@
       <div style="margin-top: 20px; margin-bottom: 20px;">
         <a href="http://www.apache.org"><img src="/assets/img/apache-foundation-logo.png" alt="Apache Incubator"/></a>
       </div>
+      <!--Footer copyright year update credit: http://updateyourfooter.com/-->
       <div>
-      Copyright &copy; 2015-2018 <a href="http://www.apache.org">The Apache Software Foundation</a>.
+      Copyright &copy; 2015<script>new Date().getFullYear()>2015&&document.write("-"+new Date().getFullYear());</script> 
+      <a href="http://www.apache.org">The Apache Software Foundation</a>.
       Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.
       <br>
       Apache and the Apache Feather logo are trademarks of The Apache Software Foundation.