Double Check 2 Credentials Tests related to mapping to urls

[aljones15]

Test/ Statement:
https://github.com/digitalbazaar/vc-data-model-2-test-suite/blob/04a307dc5e4d6686f3ca2f12054b5bba57050f3e/tests/10-vcdm2.js#L212-L226

VC:
https://github.com/digitalbazaar/vc-data-model-2-test-suite/blob/04a307dc5e4d6686f3ca2f12054b5bba57050f3e/tests/input/credential-type-unmapped-fail.json#L1-L14

Concern: this is probably failing because the type is not in a context and not because it's unmapped

VC:
https://github.com/digitalbazaar/vc-data-model-2-test-suite/blob/04a307dc5e4d6686f3ca2f12054b5bba57050f3e/tests/input/credential-type-url-ok.json#L1-L14

Concern: we generally don't use expanded forms in order to preserve interoperability with json only implementations, is this use of a url as a type ok?