DOI Parser broken

Apparently the crossref API which gets used under the hood by doi.org when querying for BibTeX data has introduced some recent changes which result in faulty labels and missing journal information. The only other mention of this, confirming my suspicions, which I could find is this issue on Github.

This causes the unittests of the DOI parser to fail and renders the DOI parser slightly awkward to use, in general (unless a default label style (config.database.format.label_default) has been configured).

I will disable the failing unittests for now but maybe a move towards the unprocessed json returned by Accept: application/citeproc+json is desirable?