Dodano testy dla liczb: 2, 3

PrimeFactorsSpec.php

<?php
    public function it_returns_2_for_2()
    {
        $this->factorize(2)->shouldReturn([2]);
    }

    public function it_returns_3_for_3()
    {
        $this->factorize(3)->shouldReturn([3]);
    }
}