_links options are http instead of https for ontologies

[Pooya-Oladazimi]

Describe the bug
In ontology metadata, there is a _links metadata that includes all the links for an ontology such as root terms. All of them are HTTP:
https://api.terminology.tib.eu/api/ontologies/agro

Expected behavior
they should be HTTPS

Additional context
this is not urgent but it may raise CORS error in a client app using the API.