math/py-graphillion: Update to 1.2

This version fixes build failures on FreeBSD versions that use Clang 6:

src/graphillion/zdd.cc:461:31: error: invalid operands to binary expression ('std::1::ostream' (aka 'basic_ostream<char>') and 'std::1::ostream')

if (out == std::cout || out == std::cerr)
                        ~~~ ^  ~~~~~~~~~

Reported by: pkg-fallout
MFH: 2018Q4