Fix missing folder master icon

gui/index.html

@@ -249,7 +249,7 @@
                       </td>
                     </tr>
                     <tr ng-if="folder.readOnly">
-                      <th><span class="fa fa-fw lock"></span>&nbsp;<span translate>Folder Master</span></th>
+                      <th><span class="fa fa-fw fa-lock"></span>&nbsp;<span translate>Folder Master</span></th>
                       <td class="text-right">
                         <span translate>Yes</span>
                       </td>