Move php_codesniffer to dev requirements

Author: stof

composer.json

@@ -14,13 +14,13 @@
     },
     "require": {
         "php": "^5.5 || ^7.0",
-        "zendframework/zend-eventmanager": "^2.6 || ^3.0",
-        "squizlabs/php_codesniffer": "^2.5"
+        "zendframework/zend-eventmanager": "^2.6 || ^3.0"
     },
     "require-dev": {
         "ext-phar": "*",
         "doctrine/annotations": "~1.0",
         "zendframework/zend-stdlib": "~2.7",
+        "squizlabs/php_codesniffer": "^2.5",
         "phpunit/PHPUnit": "^4.8.21"
     },
     "suggest": {