Do not require peer review type to present peer review data

[markwoodhall]

This commit makes it so that no peer review type node is required in order to present peer review data over the API. Data will now be presented as long as there is at least a single review data item to present. This resolves issue https://github.com/CrossRef/rest-api-doc/issues/367

[afandian]

Is there a test case for the change in behaviour? The EDN files look like they've changed but no XML changes.