Update badge to a supported SSP-version

Author: tvdijen

README.md

@@ -13,7 +13,7 @@ Currently supported flows are:
 
 [![Build Status](https://github.com/simplesamlphp/simplesamlphp-module-oidc/actions/workflows/test.yaml/badge.svg)](https://github.com/simplesamlphp/simplesamlphp-module-oidc/actions/workflows/test.yaml) 
 [![Coverage Status](https://codecov.io/gh/simplesamlphp/simplesamlphp-module-oidc/branch/master/graph/badge.svg)](https://app.codecov.io/gh/simplesamlphp/simplesamlphp-module-oidc)
-[![SimpleSAMLphp](https://img.shields.io/badge/simplesamlphp-1.19-brightgreen)](https://simplesamlphp.org/)
+[![SimpleSAMLphp](https://img.shields.io/badge/simplesamlphp-2.1-brightgreen)](https://simplesamlphp.org/)
 
 ![Main screen capture](docs/oidc.png)