null_model_und_sign casting error

[MuriloSchaefer]

Hi,

I tried to use the null_model_und_sign function to generate null-models, but it gave me the error:

slice-indices-must-be-integers-or-none-or-have-index-method

This error is related to the issue #68

Then I looked at the code and found that the variable wei_period was rounded, but it remains as float, and it was used as a vector index, so I cast it to int and the function worked well.

Thanks for the amazing work here,
Murilo Schaefer