SW5.4 compability

[OeRnY]

I added the guzzle dependency according to the current shopware stable version 5.4.0 - 5.4.6 at the time of this pull request.

Otherwise the error log would show up something like this when someone is trying to open the plugin manager within the backend view.

PHP Fatal error: Uncaught TypeError: Argument 3 passed to GuzzleHttp\Client::request() must be of the type array, string given, called in /path/to/your/shopware/custom/plugins/SwagMediaS3/vendor/guzzlehttp/guzzle/src/Client.php on line 89

This is the corresponding commit: shopware/shopware (aec725b1cd7ba4eb8b2c4001695adb3b4248df5c)