Impress Menu -> Insert -> Slide Number fixed wrong command

Impress
Menubar -> Insert -> Slide Number open the Header and Fooder Dialog

Change-Id: Ie6c03358254265422ef2b760aa182515a44480d4
Reviewed-on: https://gerrit.libreoffice.org/56976
Tested-by: Jenkins
Reviewed-by: Heiko Tietze <tietze.heiko@gmail.com>

sd/uiconfig/simpress/menubar/menubar.xml

@@ -240,7 +240,7 @@
                 </menu:menupopup>
             </menu:menu>
             <menu:menuseparator/>
-            <menu:menuitem menu:id=".uno:InsertSlideNumber"/>
+            <menu:menuitem menu:id=".uno:InsertSlideField"/>
             <menu:menu menu:id=".uno:FieldMenu">
                 <menu:menupopup>
                     <menu:menuitem menu:id=".uno:InsertDateFieldFix"/>