DX: Improve internal dist config for Fixer

[Wirone]

Utilise chained calls fully, without defining intermediate variables before.

[Wirone]

FYI: this change is inspired by my local version of the config (.php-cs-fixer.php), I just moved some of the changes to the dist file.

If you're not familiar, you can do something like this in your own config:

<?php

declare(strict_types=1);

use PhpCsFixer\Runner\Parallel\ParallelConfig;

ini_set('memory_limit', '-1');

/** @var \PhpCsFixer\Config $config */
$config = require __DIR__. '/.php-cs-fixer.dist.php';

return $config
//    ->setParallelConfig(ParallelConfig::detect())
    ->setFinder(
        $config
            ->getFinder()
            ->notPath([
                '.php-cs-fixer.php',
                'reproducer.php',
            ])
    )
;

[coveralls]

coverage: 96.053%. remained the same
when pulling 66ed06d on Wirone:codito/improve-fixer-dist-config
into f40f18e on PHP-CS-Fixer:master.