PHP 8.1 compatibility fixes

What's Changed

• Replace dirname(__FILE__) with __DIR__ by @macbre in #154
• cs-fixer: use new rules by @macbre in #155
• CI - do not fail on Coveralls uploads by @macbre in #168
• Router - fix passing null to parameter #1 ($string) of type string is deprecated by @macbre in #167

And:

• Bump phpstan/phpstan from 1.8.5 to 1.8.6 by @dependabot in #157
• Bump phpunit/phpunit from 9.5.24 to 9.5.25 by @dependabot in #158
• Bump phpstan/phpstan from 1.8.6 to 1.8.7 by @dependabot in #159
• Bump phpstan/phpstan from 1.8.7 to 1.8.8 by @dependabot in #160
• Bump predis/predis from 2.0.2 to 2.0.3 by @dependabot in #161
• Bump phpstan/phpstan from 1.8.8 to 1.8.9 by @dependabot in #162
• Bump phpstan/phpstan from 1.8.9 to 1.8.10 by @dependabot in #163
• Bump phpstan/phpstan from 1.8.10 to 1.8.11 by @dependabot in #164
• Bump phpunit/phpunit from 9.5.25 to 9.5.26 by @dependabot in #165

Full Changelog: v0.7.0...v0.8.0