ejabberd_admin: Fix ejabberd_piefxis commands

These days, the ejabberd_piefxis commands expect their arguments to be
handed over as binary strings.

src/ejabberd_admin.erl

@@ -254,19 +254,19 @@ get_commands_spec() ->
 			module = ejabberd_piefxis, function = import_file,
 			args_desc = ["Full path to the PIEFXIS file"],
 			args_example = ["/var/lib/ejabberd/example.com.xml"],
-			args = [{file, string}], result = {res, rescode}},
+			args = [{file, binary}], result = {res, rescode}},
      #ejabberd_commands{name = export_piefxis, tags = [mnesia],
 			desc = "Export data of all users in the server to PIEFXIS files (XEP-0227)",
 			module = ejabberd_piefxis, function = export_server,
 			args_desc = ["Full path to a directory"],
 			args_example = ["/var/lib/ejabberd/"],
-			args = [{dir, string}], result = {res, rescode}},
+			args = [{dir, binary}], result = {res, rescode}},
      #ejabberd_commands{name = export_piefxis_host, tags = [mnesia],
 			desc = "Export data of users in a host to PIEFXIS files (XEP-0227)",
 			module = ejabberd_piefxis, function = export_host,
 			args_desc = ["Full path to a directory", "Vhost to export"],
 			args_example = ["/var/lib/ejabberd/", "example.com"],
-			args = [{dir, string}, {host, string}], result = {res, rescode}},
+			args = [{dir, binary}, {host, binary}], result = {res, rescode}},
 
      #ejabberd_commands{name = delete_mnesia, tags = [mnesia],
                         desc = "Delete elements in Mnesia database for a given vhost",