Update footer.html

docs/_includes/footer.html

@@ -1,7 +1,7 @@
     <footer>
       <div class="container-fluid">
         <div class="row-fluid">
-			<p align="center">Copyright &copy; 1999-2020 <a class="external" href="https://shimingxy.github.io/MaxKey/">https://github.com/shimingxy/MaxKey/ </a>. All Rights Reserved.<br>
+			<p align="center">Copyright &copy; 2019-2020 <a class="external" href="https://shimingxy.github.io/MaxKey/">https://github.com/shimingxy/MaxKey/ </a>. All Rights Reserved.<br>
 		          	Licensed under the Apache License, Version 2.0
 			</p>
 		</div>