Fix nav items alignment when on multiple lines

lib/site_template/_sass/_layout.scss

@@ -35,9 +35,9 @@
         color: $text-color;
         line-height: $base-line-height;
 
-        // Gaps between nav items, but not on the first one
-        &:not(:first-child) {
-            margin-left: 20px;
+        // Gaps between nav items, but not on the last one
+        &:not(:last-child) {
+            margin-right: 20px;
         }
     }