Add PHPStan 1.0 compatibility

[jdecool]

Fix #22

PHPStan 1.0 has been released.
This PR add compatibility with PHPStan 1.0

[Wirone]

Really looking forward into this since we're currently upgrading to PHPStan 1.0 and we need this package too. I was able locally to override Composer requirements with forked version (custom github repository entry in composer.json), test and clean baseline files from errors reported before, but our setup does not work well with this for daily usage (we use Private Packagist and for now we don't have proper flow for delivering auth data for Github API) so I really need to switch constraints to stable release of this package to finish our upgrade process. Please merge it and release new stable tag 🙏

[Wirone]

@samizdam @rincler @dmitrivereshchagin @anwinged sorry for pinging but I need to ask is it possible to process this PR? Because I'm stuck with huge merge request (moving to PHPStan 1.0) in our big, monolith app which is hard to maintain in terms of all changes that are made day by day. I really would like to finish it and this package's stable version is required for that.

[samizdam]

Hi!
I release it with https://github.com/timeweb/phpstan-enum/releases/tag/v3.0.0

[Wirone]

Thank you very much @samizdam! 🍻

[jdecool]

Thanks !