The command like "subplot" doesn't work

[goldbattle]

Need to verify what versions / ubuntu version this happens on.

Details: lava/matplotlib-cpp#310

The fix is to update the subplot function:

PyTuple_SetItem(args, 0, PyLong_FromLong(nrows));
PyTuple_SetItem(args, 1, PyLong_FromLong(ncols));
PyTuple_SetItem(args, 2, PyLong_FromLong(plot_number));