Update SimpleSAMLPHP SAML2 library to 3.1.2
Update SimpleSAMLPHP SAML2 library to 3.1.2

Version 3.1.0 was vulnerable and triggered the security checker. For
more information:

CVE-2018-6519: Denial of Service in timestamp validation function
 https://simplesamlphp.org/security/201801-01

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