Update index.html

Update 3.4.0

Author: Hir0

downloads/index.html

@@ -7,7 +7,7 @@
   <div>
     <h2>Downloads</h2>
     <p>
-      <b>Current stable</b>: <a href="https://github.com/mruby/mruby/archive/3.4.0.zip">mruby 3.3.0</a>
+      <b>Current stable</b>: <a href="https://github.com/mruby/mruby/archive/3.4.0.zip">mruby 3.4.0</a>
     </p>
   </div>
 </div>