Incorrect Python version

[reidfaiv]

Section 1.2 declares Python version 3.5.2 however section 2.1 "vectorized approach" uses random.choices() function which was introduced in Python 3.6.

https://docs.python.org/3.6/library/random.html#random.choices

[rougier]

It has been introduced with issue #37. Previous version was steps = random.sample((-1, +1)*n, n)
I'll revert to previous version. According to Python documentation it is equivalent to a shuffle.

[rougier]

Done.