Not working with Ruby 2.6.6 in a Rails 6 project?

[viktorsmari]

I tried installing in a Rails 6.0.3.4 projects Gemfile like this:

gem 'goal_seeker', git: 'https://github.com/nuk/goal_seeker'

And then I access the console rails c

irb(main):005:0> GoalSeeker
=> GoalSeeker

And when trying to run the README example:

irb(main):006:0>   GoalSeeker.seek(
irb(main):007:1*     start: 100,
irb(main):008:1*     goal: 0,
irb(main):009:1*     max_cycles:100,
irb(main):010:1*     function: lambda { |x| x*x -5*x + 6 }
irb(main):011:1>   )
Traceback (most recent call last):
        1: from (irb):6
ZeroDivisionError (divided by 0)

Can anyone help debug?