Bump onelogin/php-saml from 3.8.0 to 3.8.1 (#529)

Bumps [onelogin/php-saml](https://github.com/SAML-Toolkits/php-saml) from 3.8.0 to 3.8.1.
- [Release notes](https://github.com/SAML-Toolkits/php-saml/releases)
- [Changelog](https://github.com/SAML-Toolkits/php-saml/blob/3.8.1/CHANGELOG)
- [Commits](SAML-Toolkits/php-saml@3.8.0...3.8.1)

---
updated-dependencies:
- dependency-name: onelogin/php-saml
  dependency-version: 3.8.1
  dependency-type: direct:production
...

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