Update main.html

update to lastest version.

Author: iaiti

views/main.html

@@ -278,7 +278,7 @@
 
   <footer class="main-footer">
     <div class="float-right d-none d-sm-block">
-      <b>Version</b> 4.8.0
+      <b>Version</b> 4.9.1
     </div>
     <strong>PrometheusAlert <a href="https://github.com/feiyu563/PrometheusAlert">Github</a> && <a href="https://gitee.com/feiyu563/PrometheusAlert">Gitee</a> </strong>
   </footer>