po4a/po4a.conf: Sort the language identifiers in alphabetical order.

po4a/po4a.conf

@@ -2,7 +2,7 @@
 # to get a new .po file. After translating the .po file, run
 # "update-po" again to generate the translated man pages.
 
-[po4a_langs] de fr ro uk ko pt_BR
+[po4a_langs] de fr ko pt_BR ro uk
 [po4a_paths] xz-man.pot $lang:$lang.po
 
 [type: man] ../src/xz/xz.1              $lang:man/$lang/xz.1