Bugfix

Fixes problem with following error 

php artisan scheduled:run
exception 'Illuminate\Container\BindingResolutionException' with message 'Unresolvable dependency resolving [Parameter #0 [ <required> $expression ]] in class Cron\CronExpression' in /Users/MacBook/Documents/Projects/gas/vendor/laravel/framework/src/Illuminate/Container/Container.php:841

CronExpression doesn't play well with laravel's DI.