Turn off autocomplete on "Add collaborator" form

You have already created js autocomplete for that input, so it is good to turn off the browser autocomplete. If there are more forms that have custom autocomplete, this change should be applied to them, too.

src/main/twirl/settings/collaborators.scala.html

@@ -18,7 +18,7 @@
       }
     </ul>
     @if(!isGroupRepository){
-      <form method="POST" action="@url(repository)/settings/collaborators/add" validate="true">
+      <form method="POST" action="@url(repository)/settings/collaborators/add" validate="true" autocomplete="off">
         <div>
           <span class="error" id="error-userName"></span>
         </div>