Add missing ref to Mongolian dictionary icon in Dictionary_mn.mk

Change-Id: I1a50615c6e5c7e6502bc62e66b8bc228376be356
Reviewed-on: https://gerrit.libreoffice.org/c/dictionaries/+/139981
Tested-by: Julien Nabet <serval2412@yahoo.fr>
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>

Author: serval2412

Dictionary_mn.mk

@@ -15,6 +15,7 @@ $(eval $(call gb_Dictionary_add_root_files,dict-mn,\
 	dictionaries/mn_MN/README_mn_MN.txt \
 	dictionaries/mn_MN/mn_MN.aff \
 	dictionaries/mn_MN/mn_MN.dic \
+        dictionaries/mn_MN/DictMN.png \
 ))
 
 # vim: set noet sw=4 ts=4: