remove unnecessary use of interpolation

[JimPrudent]

interp1d is by default a linear interpolation

https://github.com/scipy/scipy/blob/v1.7.0/scipy/interpolate/interpolate.py#L332-L721

[arvkevi]

Thanks for the PR @JimPrudent. My Travis CI was outdated, so the unit tests weren't run in the Travis environment. I think I've fixed the issue. I checked out your branch locally and all the unit tests passed.

Can you add an empty commit to trigger the build, something like: git commit --allow-empty -m "Trigger Build"

[codecov[bot]]

Codecov Report

Merging #97 (6d80768) into master (63a8bac) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #97   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            5         5           
  Lines          210       210           
=========================================
  Hits           210       210           

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
kneed/knee_locator.py	100.00% <100.00%> (ø)