[gimp] app: add mnemonic to the layer-group previews prefrences option

[Ell <ell src gnome org>]

commit da1558d0c8431f4fa3fc846e6a6505b92fe34451
Author: Ell <ell_se yahoo com>
Date:   Tue Jul 3 00:32:32 2018 -0400

    app: add mnemonic to the layer-group previews prefrences option

 app/dialogs/preferences-dialog.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/app/dialogs/preferences-dialog.c b/app/dialogs/preferences-dialog.c
index 7d51a12ca3..55179ec9ba 100644
--- a/app/dialogs/preferences-dialog.c
+++ b/app/dialogs/preferences-dialog.c
@@ -1747,7 +1747,7 @@ prefs_dialog_new (Gimp       *gimp,
                           vbox3,  "sensitive",
                           G_BINDING_SYNC_CREATE);
   button = prefs_check_button_add (object, "group-layer-previews",
-                                   _("Enable layer group previews"),
+                                   _("Enable layer _group previews"),
                                    GTK_BOX (vbox3));
 
   grid = prefs_grid_new (GTK_CONTAINER (vbox2));