Commit cb72f9a773e0931ee3758c851d96007ded034e4c changed the semantics of
SITE-PACKAGES, but did not adjust all callers.
* gnu/packages/bioinformatics.scm (python-pyvcf)[arguments]: Adjust for
missing trailing slash.
* gnu/packages/maths.scm (nomad-optimizer)[arguments]: Likewise.
* gnu/packages/patchutils.scm (patchwork)[arguments]: Likewise.