Update for 2.1.1

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/2.1.0.zip">mruby 2.1.0</a>
+      <b>Current stable</b>: <a href="https://github.com/mruby/mruby/archive/2.1.1.zip">mruby 2.1.1</a>
     </p>
   </div>
 </div>