Retrieves response available options from ruby-saml

[mberlanda]

In SAML-Toolkits/ruby-saml#454 was introduced a whitelisting for allowed Response options.

In my previous pr #159 I added one more option.
According to me, this whitelist introduced in 4712e99 should not be a responsibility of omniauth-saml but it should be provided out of the box by ruby-saml. It looked like @md5 agreed on this point (#159 (comment))

Since 'ruby-saml' ~>1.8 integrated this change, I updated the dependency of this gem and retrieved response available options from it.

[coveralls]

Coverage remained the same at 100.0% when pulling 3177cf1 on mberlanda:mberlanda/inherit-response-available-options into d530da4 on omniauth:master.

[mberlanda]

hey @md5 @supernova32 , do you have any feedback on this pr?

[suprnova32]

@mberlanda thanks for the ping, and thanks for the PR. I think it looks good, and I'm inclined to merge it. I'll wait until tomorrow, so that if @md5, or any one else has any objections, they can let us know.

[md5]

LGTM 👍