Fix shell script markdown code block definition

Author: antonkomarev

CONTRIBUTING.md

@@ -21,7 +21,7 @@ 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
 ```
 

README.md

@@ -41,7 +41,7 @@ PHP Weblog Contracts provides set of interfaces for the Framework Interoperable
 
 First, pull in the package through Composer.
 
-```sh
+```shell script
 $ composer require cybercog/php-contracts-weblog
 ```