replace removed scipy.interpolate.spline
scipy.interpolate.spline was deprecated in 0.19.0 and removed in 1.3.0 see here.
This is used for the calibration plotting.
I updated the call to scipy.interpolate.spline to use scipy.interpolate.interp1d.
This is the same method as is used in the calibration module.
We may want to make a change down the line to make the plotting use the code from the calibration module.
This is currently broken in the current ligo cvmfs builds so we should fix ASAP.