Remove redundant async option from iframe-render

Author: Vladyslav Tymofeiev

lms/templates/main.html

@@ -48,7 +48,7 @@
       </title>
   </%block>
 
-  <script async type="text/javascript" src="${static.url("lms/js/iframe-render.js")}"></script>
+  <script type="text/javascript" src="${static.url("lms/js/iframe-render.js")}"></script>
 
   % if not allow_iframing:
       <script type="text/javascript">