Adapt to imewlconverter's GNU-style command line.

app-text/imewlconverter dropped the legacy "-i:fmt in -o:fmt out" argument
syntax in favour of GNU-style options, and it no longer recurses a directory
passed as input (a directory argument now yields an empty dictionary and exit
0). Convert the scel folder explicitly through the .scel files and the new
"-i fmt -o fmt -O out inputs..." form.

Not accepted upstream; the upstream Makefile still uses the old syntax.

--- a/Makefile
+++ b/Makefile
@@ -8,11 +8,11 @@

 sougou.source.fcitx:
 	test -d sougou_dict || { echo The sougou_dict folder does not exist!; exit 1; }
-	ImeWlConverterCmd -i:scel sougou_dict -o:libimetxt sougou.source.fcitx
+	ImeWlConverterCmd -i scel -o libimetxt -O sougou.source.fcitx sougou_dict/*/*.scel

 sougou.source.rime:
 	test -d sougou_dict || { echo The sougou_dict folder does not exist!; exit 1; }
-	ImeWlConverterCmd -i:scel sougou_dict -o:rime sougou.source.rime
+	ImeWlConverterCmd -i scel -o rime -O sougou.source.rime sougou_dict/*/*.scel

 sougou.dict: sougou.source.fcitx
 	libime_pinyindict sougou.source.fcitx sougou.dict