update copyright year

Author: jube

index.html

@@ -39,7 +39,7 @@ <h3>gf 1.2.0 (14 Jul 2023)</h3>
 
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-        <p><a href="https://opensource.org/licenses/Zlib">Copyright</a> &copy; 2016-2018 <a href="https://github.com/jube">Julien Bernard</a></p>
+        <p><a href="https://opensource.org/licenses/Zlib">Copyright</a> &copy; 2016-2023 <a href="https://github.com/jube">Julien Bernard</a></p>
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