Import polyfit/val from numpy

[TheSkyentist]

Import polyval from numpy instead of scipy to fix mitigate issues.

[gbrammer]

I think it would be safest to

from numpy.polynomial.polynomial import polyfit, polyval

rather than from the general numpy namespace with from numpy import polyfit, polyval.

[TheSkyentist]

Good idea, I've committed the requested changes.

[gbrammer]

Thanks!