gui: HTML accessibility updates

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4258
LGTM: calmh

gui/default/syncthing/transfer/failedFilesModalView.html

@@ -14,7 +14,7 @@
     <ul class="pagination pull-right">
       <li ng-repeat="option in [10, 25, 50]" ng-class="{ active: failedPageSize == option }">
         <a href="#" ng-click="failedChangePageSize(option)">{{option}}</a>
-      <li>
+      </li>
     </ul>
     <div class="clearfix"></div>
   </div>