update offline reference download link

Author: Qianqianye

src/yuidoc-p5-theme-src/scripts/tpl/menu.html

@@ -1,7 +1,7 @@
 <div>
   <br>
   <span id="reference-description1">Can't find what you're looking for? You may want to check out</span>
-  <a href="#/libraries/p5.sound">p5.sound</a>.<br><a href='https://p5js.org/offline-reference/p5-reference.zip' target=_blank><span id="reference-description3">You can also download an offline version of the reference.</span></a>
+  <a href="#/libraries/p5.sound">p5.sound</a>.<br><a href='https://archive.p5js.org/offline-reference/p5-reference.zip' target=_blank><span id="reference-description3">You can also download an offline version of the reference.</span></a>
 </div>
 
 <div id='collection-list-categories'>