replace PSR-2 in README.md with PSR-12 #8

Author: gregor-j

README.md

@@ -7,10 +7,10 @@ This repository defines interfaces for implementing the [PHP/SAP][phpsap] API.
 
 ## Coding standards
 
-This project uses [PSR-2] coding standard and [PHP_CodeSniffer] for validations.
+This project uses [PSR-12] coding standard and [PHP_CodeSniffer] for validations.
 In order to validate before a commit, call `vendor/bin/phpcs`.
 
 [phpsap]: https://php-sap.github.io
 [license-mit]: https://img.shields.io/badge/license-MIT-blue.svg
-[PSR-2]: https://www.php-fig.org/psr/psr-2/
+[PSR-12]: https://www.php-fig.org/psr/psr-12/
 [PHP_CodeSniffer]: https://github.com/squizlabs/PHP_CodeSniffer