Outdated 'nubKey' values

[janneadolf]

Looking at the data rows for which 'taxonomicStatus' == 'ACCEPTED' and using rgbif::name_backbone_checklist() with the checklist's scientific names, I find that a few 'nubKey' values seem to no longer be up to date.
This concerns the following values, which are now associated with status 'SYNONYM' or 'DOUBTFUL':

'SYNONYM': 2227000, 2227064, 2706134, 2765940, 8000520, 8879526
'DOUBTFUL': 5224480