Cors does not work with `accept` header set

[GordianDziwis]

When doing a CORS request against:

"https://archivo.dbpedia.org/download?o=http://xmlns.com/foaf/0.1/&f=nt"

It does not work with a

Accept: application/n-triples, application/rdf+xml, text/turtle

header, but:

Accept: */*

works.

[JJ-Author]

prepared a commit for this f298068
can be tested on archivo.tools.dbpedia.org

I am preparing a major release of archivo (dev running on the tools server) that is using Databus 2.0. So that is why it will still need some weeks until the fix will end up with this major release on the production deployment.