Rename usage of deprecated SAML options

[MrSerth]

I started using the omniauth-saml gem a few days ago. While implementing SSO and SLO functionality, I noticed a discrepancy between the settings of the current ruby-saml gem and this gem. This MR is intended to fix these:

Deprecations

• settings.issuer has been renamed to settings.sp_entity_id with ruby-saml 1.11.0
• settings.idp_sso_target_url has been renamed to settings.idp_sso_service_url with ruby-saml 1.12.0
• settings.idp_slo_target_url has been renamed to settings.idp_slo_service_url with ruby-saml 1.12.0

While I would recommend all usages of this gem to update the settings, these changes should be backward compatible: Ruby-SAML has built-in support for using the new names to query information set with the deprecated methods:

• settings.sp_entity_id might return the value of settings.issuer
• settings.idp_sso_service_url might return the value of settings.idp_sso_target_url
• settings.idp_slo_service_url might return the value of settings.idp_slo_target_url

[MrSerth]

Sorry to ping you, @bufferoverflow and @suprnova32, directly. I just wanted to ask for feedback for my PR and would appreciate if you could have a look to potentially merge these changes and release a new version of the gem. Thanks a lot for your time and please excuse reaching out to you.

[bufferoverflow]

looks good to me but we miss CI at the moment here. I prefer to have this in place before doing any merge.

[suprnova32]

@MrSerth I set up GitHub Actions for CI just now. If you rebase your changes against master we should see the tests running for your branch as well.

[suprnova32]

v2.1.0 has been pushed to include these changes

[MrSerth]

Awesome, thank you for introducing the CI and pushing a new release! 👏