Custom client being reset after Telegram initialisation

[noplanman]

Bug Report

Required Information

?	!
PHP Telegram Bot version	0.59.0

Summary

When setting a custom client via Request::setClient(...) before initialising the Telegram object, it gets overwritten.

Current behaviour

Custom client get overwritten.

How to reproduce

// Set custom client.
Request::setClient(new GuzzleHttp\Client([
    'base_uri' => 'https://api.telegram.org',
    'proxy'    => $proxy_url,
]));
// Create Telegram API object.
$telegram = new Telegram($bot_api_key, $bot_username);

Expected behaviour

Custom client should be remembered.