fix version dropdown in docs

docs/_includes/navbar.html

@@ -9,7 +9,7 @@
       </a>
       <div class="dropdown-menu py-0" aria-labelledby="navbarVersionDropdown">
         <a class="dropdown-item bg-info disabled" href="#">v3.1</a>
-        <a class="dropdown-item bg-info disabled" href="https://adminlte.io/docs/3.0/">v3.0</a>
+        <a class="dropdown-item" href="https://adminlte.io/docs/3.0/">v3.0</a>
         <div class="dropdown-divider"></div>
         <a class="dropdown-item" href="https://adminlte.io/docs/2.4/installation">v2.4</a>
         <a class="dropdown-item" href="https://adminlte.io/themes/AdminLTE/documentation/index.html">&lt;= v2.3</a>