Declare using PER-CS2.0

Author: alies-dev

.github/CONTRIBUTING.md

@@ -44,7 +44,7 @@ Before submitting a pull request:
 
 If the project maintainer has any additional requirements, you will find them listed here.
 
-- **[PSR-2 Coding Standard](https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-2-coding-style-guide.md)** - The easiest way to apply the conventions is to install [PHP Code Sniffer](https://pear.php.net/package/PHP_CodeSniffer).
+- **[PER-CS2.0 Coding Standard](https://github.com/php-fig/per-coding-style/blob/master/spec.md)** - The easiest way to apply the conventions is to install [PHP Code Sniffer](https://pear.php.net/package/PHP_CodeSniffer).
 - **Add tests!** - Your patch won't be accepted if it doesn't have tests.
 - **Document any change in behaviour** - Make sure the `README.md` and any other relevant documentation are kept up-to-date.
 - **Consider our release cycle** - We try to follow [SemVer v2.0.0](https://semver.org/). Randomly breaking public APIs is not an option.