Use new shibboleth Maven repository URL

```
As of 20 January 2022, the following Maven repository URLs are being redirected : 
https://build.shibboleth.net/nexus/content/groups/public  
to
https://build.shibboleth.net/maven/releases 
```

see https://shibboleth.atlassian.net/wiki/spaces/DEV/pages/2891317253/MavenRepositories#Old-Shibboleth-Maven-Repository-URLs

Author: apupier

pom.xml

@@ -143,7 +143,7 @@
         <repository>
             <id>B_shibboleth</id>
             <name>OpenSAML</name>
-            <url>https://build.shibboleth.net/nexus/content/groups/public</url>
+            <url>https://build.shibboleth.net/maven/releases</url>
             <releases>
                 <enabled>true</enabled>
             </releases>