Change 'dl_fldigi' to 'dl-fldigi' in win32.

It changed in this merge https://github.com/richardeoin/dl-fldigi/commit/2fe29550

Thanks to @m1ari for finding this

src/main.cxx

@@ -404,7 +404,7 @@ int main(int argc, char ** argv)
 	FLMSG_dir.clear();
 
 #ifdef __WOE32__
-	size_t p = appdir.rfind("dl_fldigi.exe");
+	size_t p = appdir.rfind("dl-fldigi.exe");
 	appdir.erase(p);
 	p = appdir.find("FL_APPS\\");
 	if (p != string::npos) {