Use CURIEs in spec docs

[cmungall]

The spec mentions CURIEs, but includes examples like this:

https://github.com/ga4gh-discovery/data-connect/blob/develop/SPEC.md#search-example

Request body:
{
  "query": "SELECT * from search_postgres_pgpc.ontology.axiom WHERE to_term=?"
  "parameters": [ "UBERON_0000464" ]
}

I would recommend using the UBERON CURIE, i.e. UBERON:0000464 (and having a separate prefixmap that points to the OBO PURL)

Thanks, Chris (Uberon developer)