fitting error when use approximate_curve

[maozaizhou]

Describe the bug
hi, when i use the approximate_curve function to fit some 2d points, there are obvious fitting error in first few points,but it looks fitting well in the end
To Reproduce
Steps to reproduce the behavior:

1. here is the 2d points
   fitting_points.txt
2. then run some code like example
   degree = 3 curve = fitting.approximate_curve(points, degree)
   the result plot like this
   

the purple points is the original points which i want to fit , the purple line is fitting by scipy LSQUnivariateSpline , the huge difference locate in first few points

then i try revert the points order , the same error still appear in first few points like the plot show bellow

appreciate if any suggestion.

[maozaizhou]

duplicate with #120 close