Apply fixes from StyleCI

[mechelon]

This pull request applies code style fixes from an analysis carried out by StyleCI.

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[what-the-diff]

• Fixing the issue with phpdoc properties
• Adding missing slash in config path
• Removing unused code from NotionModel class and fixing some typos there as well
• Changing paginate method to return array instead of collection, so it can be used by Laravel's Paginator component (https://laravel-news.com/pagination-with-customized-keys)