Added an -ed (#1273)

Possibly the most useless pull request.

docs/documentation/elements/button.html

@@ -517,7 +517,7 @@ variables:
         <div class="message is-info">
           <div class="message-body">
             <p>
-              Since the loading spinner is implemented using the <code>:after</code> pseudo-element, it is not support by the <code>&lt;input type="submit"&gt;</code> element.
+              Since the loading spinner is implemented using the <code>:after</code> pseudo-element, it is not supported by the <code>&lt;input type="submit"&gt;</code> element.
             </p>
           </div>
         </div>