update link to Maven central

Author: ceki

logback-site/src/site/pages/download.html

@@ -38,7 +38,7 @@ <h2>Binaries in Maven central</h2>
 
     <p>Logback artifacts such as <em>.jar</em>, <em>.sources.jar</em>
     and <em>javadoc.jar</em> files can be downloaded from <a
-    href="http://repo2.maven.org/maven2/ch/qos/logback">Maven
+    href="https://repo1.maven.org/maven2/ch/qos/logback">Maven
     central</a> under the <code>ch.qos.logback</code> groupId.</p>