Update .env.example

[pxpm]

L7+ Removed mail driver to use mail mailer. From L7 upgrade guide:

In order to support multiple mailers, the default mail configuration file has changed in Laravel 7.x to include an array of mailers. However, in order to preserve backwards compatibility, the Laravel 6.x format of this configuration file is still supported. So, no changes are required when upgrading to Laravel 7.x; however, you may wish to examine the new mail configuration file structure and update your file to reflect the changes. https://github.com/laravel/laravel/blob/7.x/config/mail.php