Update simplesamlphp/saml2 to 3.1.2
Update simplesamlphp/saml2 to 3.1.2

A bug was introduced in 3.1.1 that was addressed in this version.

https://github.com/simplesamlphp/saml2/issues/112

SURFnet/Stepup-SelfService,SURFnet/Stepup-SelfService,SURFnet/Stepup-SelfService