ev-window: Fix enable caret navigation question message

https://bugzilla.gnome.org/show_bug.cgi?id=727062

shell/ev-window.c

@@ -5731,7 +5731,7 @@ ev_window_cmd_view_toggle_caret_navigation (GtkAction *action,
 					    _("Pressing F7 turns the caret navigation on or off. "
 					      "This feature places a moveable cursor in text pages, "
 					      "allowing you to move around and select text with your keyboard. "
-					      "Do you want to enable the caret navigation on?"));
+					      "Do you want to enable the caret navigation?"));
 
 	window->priv->ask_caret_navigation_check = gtk_check_button_new_with_label (_("Don't show this message again"));
 	hbox = gtk_box_new (GTK_ORIENTATION_HORIZONTAL, 12);