MFH: r424744 r424860

sysutils/py-plumbum: fix packages with Python 3

PR: 213812
Submitted by: jbeich

sysutils/py-plumbum: use autoplist instead of py3kplist.

• py3kplist should only be used if there is no alternative.
• MFH in conjuction with r424744

PR: 213812
Reported by: rm

Approved by: ports-secteam (feld@)