fix link :(

index.html

@@ -73,7 +73,7 @@ <h2>+[mulle-objc about]</h2>
       various platforms. It consists of the following parts:
       <p>
       <table>
-        <tr><th>Developer Guide</th><td><a href="https://www.mulle-kybernetik.com/De-Re-mulle-objc/">De Re mulle-objc</a></td></tr>
+        <tr><th>Developer Guide</th><td><a href="https://www.mulle-kybernetik.com/de-re-mulle-objc/">De Re mulle-objc</a></td></tr>
         <tr><td colspan=2></td></tr>
         <tr><th>Class libraries</th><td><a href="https://github.com/MulleFoundation">MulleFoundation</a><br>
                                       <a href="https://github.com/MulleWeb">MulleWeb</a></td></tr>