Fix configuration argument name in readme

action.yml says the argument is called `configuration`

Author: carlobeltrame

README.md

@@ -38,7 +38,7 @@ Inputs
 
 The following configuration options are available:
 
-+ `config` Path to the `phpunit.xml` file (default: `test/phpunit/phpunit.xml`)
++ `configuration` Path to the `phpunit.xml` file (default: `test/phpunit/phpunit.xml`)
 + `junit` Path to junit output file (default: `test/phpunit/_junit/junit.xml`)
 + `memory` The memory limit to run your tests with (default: `512M`)
 + `bootstrap` The path to the bootstrap file (default: `vendor/autoload.php`)