devel/py-stdnum: update 1.10 -> 1.13
Relnotes: https://lists.arthurdejong.org/python-stdnum-announce/2019/msg00000.html
https://lists.arthurdejong.org/python-stdnum-announce/2019/msg00001.html https://lists.arthurdejong.org/python-stdnum-announce/2020/msg00000.html