patch 8.1.2082: some files have a weird name to fit in 8.3 characters

Problem:    Some files have a weird name to fit in 8.3 characters.
Solution:   Use a nicer names.
diff --git a/src/proto/popupmnu.pro b/src/proto/popupmnu.pro
index c019663..f5b6c0c 100644
--- a/src/proto/popupmnu.pro
+++ b/src/proto/popupmnu.pro
@@ -1,4 +1,4 @@
-/* popupmnu.c */
+/* popupmenu.c */
 void pum_display(pumitem_T *array, int size, int selected);
 void pum_call_update_screen(void);
 int pum_under_menu(int row, int col);