Adding Support for Laravel 9

[cyberlightdev]

This PR "adds" support for Laravel 9 by:

• Declaring support for illuminate/encryption version ^9.0, which contains no breaking changes I am aware of.
• Adding Support for PHP 8 and 8.1 in both composer.json, as 8 is the new minimum version.
• Additing testing support for PHP ^8.0 in Travis CI.

Simple testing of php artisan credentials:edit and the crendentials(key) helper in Laravel 9 show the output working as expected. Great success?

[cyberlightdev]

Since it might take a little while for BeyondCode to merge this or do it themselves, feel free to use my forked repository by telling composer.json about it like this.

"repositories": [
{
  "type": "vcs",
  "url": "https://github.com/mknooihuisen/laravel-credentials.git"
}],
"require": {
    "php": "^8.0",
    "beyondcode/laravel-credentials": "dev-master",
    ...
}

I have no desire to replace Marcel, so, if and when I find out Official Laravel 9 support exists, I'll deprecate my version with a note to revert to the official package.

[surgiie]

This project appears no longer maintained, thanks for this.