heroku laravel 5.6 password reset mail not sending

I'm currently having trouble with the password reset mail created by make:auth in Laravel 5.6. My app is hosted on heroku. In my local environment everything works fine. I have set the right values in the config vars in heroku, same in my local .env file:

    MAIL_DRIVER=smtp
    MAIL_HOST=smtp.gmail.com
    MAIL_PORT=587
    MAIL_USERNAME=myMail@gmail.com
    MAIL_PASSWORD=bla
    MAIL_ENCRYPTION=tls

I have read here that I have to hardcode the values inside app/mail.php instead of referencing the .env file (bcs heroku wouldn't recognize/understand this reference 'password' => env('MAIL_PASSWORD').

But then my data would be visible inside the github repo.

Can someone help me, what the problem could be?

thanks in advance

via Chebli Mohamed