Fix zroots method in foton.py.in
Test case:
$ python3 -c 'import foton; foton.FilterDesign(rate=16384).zroots([0.1], [0.2], 1)'
Traceback (most recent call last):
File "<string>", line 1, in <module>
File "/usr/lib/python3/dist-packages/foton.py", line 783, in zroots
return self.filt.zroots(nzeros, zvec, npoles, pvec, gain)
TypeError: none of the 2 overloaded methods succeeded. Full details:
bool FilterDesign::zroots(int nzeros, const basicplx<double>* zero, int npoles, const basicplx<double>* pole, double gain = 1.) =>
could not convert argument 2
bool FilterDesign::zroots(int nzeros, const basicplx<float>* zero, int npoles, const basicplx<float>* pole, double gain = 1.) =>
could not convert argument 2