Please update examples to take the deprecation of idp_slo_target_url into account

[gusblack-tt]

Taken from https://github.com/SAML-Toolkits/ruby-saml/blob/07947f74fbf2f44ec361d4e5edf874f0cfd99e98/UPGRADING.md#upgrading-from-111x-to-1120

Code associated: https://github.com/SAML-Toolkits/ruby-saml-example/blob/master/app/controllers/saml_controller.rb#L65

Upgrading from 1.11.x to 1.12.0
Version 1.12.0 adds support for gcm algorithm and change/adds specific error messages for signature validations

idp_sso_target_url and idp_slo_target_url attributes of the Settings class deprecated in favor of idp_sso_service_url and idp_slo_service_url. The IdpMetadataParser#parse, #parse_to_hash and #parse_to_array methods now retrieve SSO URL and SLO URL endpoints with idp_sso_service_url and idp_slo_service_url (previously idp_sso_target_url and idp_slo_target_url respectively).