Revocation Flag Returns false when valid

[tsnyder-gs1us]

When checking Revocation for a Verifiable Credentials the library returns valid = false when the credential is not revoked. When the credential is revoked is returns valid = true. This behavior is confusing and not consistent with how the other valid flags work.

Here is an example when a Verifiable Credentials passed both the revocation and json schema validation.

[OR13]

I revised the interface for status checks here: https://github.com/transmute-industries/verifiable-credentials/pull/13

Please let me know what you think