crop ontology PURLs are incorrect

[cmungall]

As pointed out here: biopragmatics/bioregistry#527

The OLS PURLs for COs use a http + www scheme e.g. https://www.ebi.ac.uk/ols/ontologies/co_325/terms?iri=http%3A%2F%2Fwww.cropontology.org%2Frdf%2FCO_325%3A0000536

but the actual OWL from the CO site is of the form https://cropontology.org/rdf/CO_325:0000536

Possible related: #508

[henrietteharmse]

Hi Chris,

This is a known issue on OLS wrt the crop ontologies. For the last while OLS has not been able to download most of the crop ontologies. I have notified them of this as OLS seem to have no issues downloading any other ontologies.