Bump phpstan/phpstan from 0.12.86 to 0.12.87 (#44)

Bumps [phpstan/phpstan](https://github.com/phpstan/phpstan) from 0.12.86 to 0.12.87.
- [Release notes](https://github.com/phpstan/phpstan/releases)
- [Commits](phpstan/phpstan@0.12.86...0.12.87)

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