numpy shallow copy issue

[qsisi]

Hello.

https://github.com/acschaefer/polex/blob/1d1d1819578079c5d4ce05b5db2584d4f52ac864/poles/poles.py#L93-L93 This is a shallow copy of numpy array, but the code seems to need the deep copy of optcentroids[ic] -> lastcentroid, so does this need to be modified? It looks like it does not make too "much" affect on the output poleparams.