Invalid metadata when using logout endpoints #19

The produced metadata is invalid according to the XSD schema when using logout endpoints.

As shown in the schema: https://docs.oasis-open.org/security/saml/v2.0/saml-schema-metadata-2.0.xsd

A logout service is a non-indexed endpoint, thus without index attribute. Furthermore, it should appear right before NameIDService (I know, xml sucks)