referenceCategory error converting from SPDX to CycloneDX

This is the error the tool throws trying to convert from one format to other.

`The JSON value could not be converted to CycloneDX.Spdx.Models.v2_2.ExternalRefCategory. Path: $.packages[0].externalRefs[0].referenceCategory`

The SPDX file contains this section

```
"externalRefs": [
{
"referenceCategory": "PACKAGE-MANAGER",
"referenceLocator": "pkg:golang/github.com/hashicorp/go-uuid@1.0.2",
"referenceType": "purl"
}
]
```