<?php

namespace Zizaco\FactoryMuff\Kind;

use Zizaco\FactoryMuff\Kind;

class Integer extends Kind
{
    public function generate()
    {
        $length = (int) $this->getOption(0, 5);

        return $this->randomNumber($length);
    }

    private function randomNumber($length)
    {
        $integer = null;
        for ($i = 0; $i < $length; $i++) {
            $integer .= mt_rand(1, 9);
        }

        return (int) $integer;
    }
}

<?php

namespace Zizaco\FactoryMuff\Kind;

use Zizaco\FactoryMuff\Kind;

class Integer extends Kind
{
    public function generate()
    {
        $length = (int) $this->getOption(0, 5);
        return $this->faker->randomNumber($length, true);
    }
}

Use randomNumber() from faker in strict mode
Use randomNumber() from faker in strict mode
