cffconvert CITATION.cff fails validation

[mhamilt]

With cffconvert==2.0.0 the current citation validate with:

cffconvert --validate --url https://github.com/citation-file-format/cffconvert

returns

ValueError: Unrecognized value for key "cff-version".

To confirm the problem was not the install I have checked with other citation files and behaviour is normal

 cffconvert --validate --url https://github.com/citation-file-format/citation-file-format

which returns

Citation metadata are valid according to schema version 1.2.0.