Fix shell script markdown code block definition

Author: antonkomarev

CONTRIBUTING.md

@@ -21,15 +21,15 @@ Due to time constraints, we are not always able to respond as quickly as we woul
 
 This project comes with a configuration file for php-cs-fixer (.php_cs) that you can use to (re)format your sourcecode for compliance with this project's coding guidelines:
 
-```sh
+```shell script
 $ vendor/bin/php-cs-fixer fix
 ```
 
 ## PHPUnit tests
 
 The phpunit script can be used to invoke the PHPUnit test runner:
 
-```sh
+```shell script
 $ vendor/bin/phpunit
 ```
 

README.md

@@ -98,7 +98,7 @@ Helper traits will automatically cast flag attributes to a `DateTime` / `Carbon`
 
 Pull in the package through Composer.
 
-```sh
+```shell script
 $ composer require cybercog/laravel-eloquent-flag
 ```
 
@@ -122,7 +122,7 @@ Please see [CONTRIBUTING](CONTRIBUTING.md) for details.
 
 Run the tests with:
 
-```sh
+```shell script
 $ vendor/bin/phpunit
 ```