Fix - Lumen 5.5 error

[turkeryildirim]

Call to undefined method Laravel\Lumen\Application::configPath()

[turkeryildirim]

config_path and such helper functions does not provided by Lumen but on most cases (to use some popular packages) you'd have to add them into your bootstrap/app.php or a helper file. This change makes possible to use this package with lumen 5.5 with config_path added helper.