do not add the prefix "python" if already in the dependency name
do not add the prefix "python" if already in the dependency name

Packages found on PyPI can be named "python-xx" (like python-dateutil).
This was building packages with "python-python-dateutil" as dependency

djhaskin987/fpm,djhaskin987/fpm,djhaskin987/fpm,djhaskin987/fpm