Fix #40: Separator has to be first

[gartner]

In php 8 the separator needs to be the first argument to implode() - in php 7 and earlier, it could be both first and last.

[lantos1618]

yeah this commit looks right https://www.php.net/manual/en/function.implode.php

implode(array $array, string $separator): string // Legacy signature (deprecated as of PHP 7.4.0, removed as of PHP 8.0.0):

is now implode(string $separator, array $array): string