obsolete URL at sparqlfun

@cmungall https://linkml.io/sparqlfun/endpoints/#endpoint-ubergraph
gives an obsolete endpoint URL: https://stars-app.renci.org/ubergraph/sparql (the correct one is https://ubergraph.apps.renci.org/sparql)

@balhoff btw https://stars-app.renci.org/ returns some stock CentOS screen.
You may want to take that host down.

Start at the endpoint-ubergraph section of the sparqlfun documentation linked in the issue. Replace the obsolete Ubergraph endpoint reference with the correct URL, then verify that the documentation link resolves to the current endpoint and no longer points to the old host.

Written by the indexing model from the issue text.