Update GeoNode demo version links

Updated demo version links from 5.0.x to 5.1.x in index.html.

Author: giohappy

docs/index.html

@@ -41,7 +41,7 @@ <h1> Welcome to GeoNode Live Demo</h1>
       <div class="row demo-container">
 	      <div class="col-md-6">
           <h4 class="demo-stable" style="background-color: #26972d"><a href="https://stable.demo.geonode.org/">Latest stable</a></h4>
-          <span><a href="https://github.com/GeoNode/geonode/tree/5.0.x" target="_blank">5.0.x</a></span>
+          <span><a href="https://github.com/GeoNode/geonode/tree/5.1.x" target="_blank">5.1.x</a></span>
         </div>
         <div class="col-md-6">
           <h4 class="demo-stable" style="background-color: #25567B"><a href="https://development.demo.geonode.org">Development</a></h4>