fixed wrong tip at additional settings window

ubl-settings-usergroups-additional-settings.glade

@@ -84,7 +84,7 @@
                     <property name="visible">True</property>
                     <property name="can-focus">True</property>
                     <property name="secondary-icon-name">com.ublinux.ubl-settings-usergroups.profile-symbolic</property>
-                    <property name="placeholder-text" translatable="yes">superuser</property>
+                    <property name="placeholder-text" translatable="yes">superadmin</property>
                   </object>
                   <packing>
                     <property name="expand">True</property>