ensure shortname is used for filenames

One place I noticed this is here:

https://github.com/frink-okn/okn-registry/pull/119/files#diff-8925a8cffb71a60bbcf1ba3d674d63c9f2116f8267ba9eb2e9f95437175ef55dR6

We have some issues linking to graph descriptions from registry pages because of these issues.