Added Css for last menu item

Added Css for last menu item in mobile view.
Fixing processing/p5.js-website#615

Author: TheShubham99

src/assets/css/main.css

@@ -2141,6 +2141,11 @@ footer {
   #menu li {
     display: inline-block;
   }
+
+  #menu li #last::after{
+    content:".";
+  }
+
   #menu li a::after {
     content: ",";
   }