Fix 'latest release' link

Change-Id: I3148518dcab2418cf877c7700e0e8e313f72293f
diff --git a/index.md b/index.md
index 102cc2c..16e5161 100644
--- a/index.md
+++ b/index.md
@@ -66,7 +66,7 @@
                 <div class="panel-body">
                     <h4>Download</h4>
                     <p>Our latest release is:<br>
-                    <b><a href="2.15.md">2.15.3</a></b>
+                    <b><a href="2.15.html">2.15.3</a></b>
                     </p>
                     <a href="https://gerrit-releases.storage.googleapis.com/gerrit-2.15.3.war" class="btn btn-primary">Download</a>
                 </div>