Update css4j download URLs

Author: carlosame

index.html

@@ -55,9 +55,9 @@ <h2>Downloads</h2>
 <div class="subtema">
 <h3>Core module</h3>
 <ul>
-<li><a href="https://github.com/css4j/css4j/releases/download/v5.3.1/css4j-5.3.1.zip">Release 5.3.1 download</a>. <a href="https://sourceforge.net/projects/carte/files/css4j/5.x/css4j-5.3.1.zip/download">[mirror]</a> <a href="digest/css4j-5.3.1.sha256"><code>[SHA256]</code></a> <a href="digest/css4j-5.3.1.sha1"><code>[SHA1]</code></a> <a href="digest/css4j-5.3.1.b2"><code>[B2]</code></a> <a href="digest/css4j-5.3.1.md5"><code>[MD5]</code></a></li>
+<li><a href="https://github.com/css4j/css4j/releases/download/v6.0/css4j-6.0.zip">Release 6.0 download</a>. <a href="https://sourceforge.net/projects/carte/files/css4j/6.x/css4j-6.0.zip/download">[mirror]</a> <a href="digest/css4j-6.0.sha256"><code>[SHA256]</code></a> <a href="digest/css4j-6.0.sha1"><code>[SHA1]</code></a> <a href="digest/css4j-6.0.b2"><code>[B2]</code></a> <a href="digest/css4j-6.0.md5"><code>[MD5]</code></a></li>
 <li><a href="https://sourceforge.net/projects/carte/files/css4j/digest/">Digest mirror</a>.</li>
-<li><a href="https://github.com/css4j/css4j/blob/v5.3.1/RELEASE_NOTES.md">Release Notes for 5.3.1</a>.</li>
+<li><a href="https://github.com/css4j/css4j/blob/v6.0/RELEASE_NOTES.md">Release Notes for 6.0</a>.</li>
 </ul>
 </div>
 <div class="subtema">