Fix PURL for CREDIT

[marijane]

It needs to end in .owl. Prerequisite for #9.

[marijane]

I looked into this, and I was wrong, it does not need to end in .owl -- I maintain URLs at purl.org for other ontologies that don't end in .owl and they import in Protege just fine. I have reached out to the w3id.org mailing list to figure out why the credit URL doesn't work as an import.

This means I am technically blocked, but we can always switch to purl.org if it looks like w3id.org is not going to work out.

[marijane]

This has been fixed and I have released a new version of the credit-ontology: https://github.com/data2health/credit-ontology/releases/tag/v2019-04-01

[marijane]

Today someone got back to me on the w3id.org list.

• They noted that the http://w3id.org/credit/ontology works fine in Protege 5.5.
• I had been experiencing the import issue with Protege 5.2.
• I upgraded to Protege 5.5. Indeed, the import works in this version.

This raises a question: do we want to switch back to w3id.org, or stick with purl.org?

• w3id.org is believed to be more stable, but it would mean people running old proteges would have problems importing the ontology.
• purl.org may be less stable, but it works with older versions of protege.
• there are differing opinions on what version of protege most people are likely to be running. my experience is that people do not upgrade right away, and that there is some hesitance to upgrade because new versions of protege have a history of breaking things that used to work.

After consulting with @nicolevasilevsky and @mbrush, for now we are going to stick with purl.org.

• it's less work for now to not switch back
• we can always go back to w3id.org in the future
• i'm not going to delete either redirect so they will both work regardless