Fix dropup example code

docs/4.0/components/dropdowns.md

@@ -387,9 +387,8 @@ Trigger dropdown menus above elements by adding `.dropup` to the parent element.
 {% highlight html %}
 <!-- Default dropup button -->
 <div class="btn-group dropup">
-  <button type="button" class="btn btn-secondary">Dropup</button>
   <button type="button" class="btn btn-secondary dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
-    <span class="sr-only">Toggle Dropdown</span>
+    Dropup
   </button>
   <div class="dropdown-menu">
     <!-- Dropdown menu links -->