cumul_integrate gives wrong result?

```julia
julia> x = collect(1.0:5.0)
5-element Vector{Float64}:
1.0
2.0
3.0
4.0
5.0

julia> y = x.^2
5-element Vector{Float64}:
1.0
4.0
9.0
16.0
25.0

julia> cumul_integrate(x, y)
5-element Vector{Float64}:
2.5
5.0
11.5
24.0
44.5
```

The result is different from
https://www.mathworks.com/help/matlab/ref/cumtrapz.html

Should we expect an array like `[2.5, 9.0, 21.5, 42.0]` from `cumul_integrate`?