Add support for Laravel 9

[dbhynds]

Description

Adds support for Laravel 9

Motivation and context

Laravel 9 has been released, but this package doesn't support it.

How has this been tested?

I didn't do any automated testing here, but I'm using this branch on our app which has extensive automated tests and they all pass.

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

Go over all the following points, and put an x in all the boxes that apply.

Please, please, please, don't send your pull request until all of the boxes are ticked. Once your pull request is created, it will trigger a build on our continuous integration server to make sure your tests and code style pass.

• [x] I have read the CONTRIBUTING document.
• [x] My pull request addresses exactly one patch/feature.
• [x] I have created a branch for this patch/feature.
• [x] Each individual commit in the pull request is meaningful.
• [ ] I have added tests to cover my changes.
• [ ] If my change requires a change to the documentation, I have updated it accordingly.

If you're unsure about any of these, don't hesitate to ask. We're here to help!