move athletic library into require-dev section in composer

Author: Michał Bundyra

composer.json

@@ -14,8 +14,7 @@
     },
     "require": {
         "php": ">=5.5",
-        "zendframework/zend-stdlib": "~2.5",
-        "athletic/athletic": "dev-master"
+        "zendframework/zend-stdlib": "~2.5"
     },
     "minimum-stability": "dev",
     "prefer-stable": true,
@@ -33,6 +32,7 @@
     },
     "require-dev": {
         "fabpot/php-cs-fixer": "1.7.*",
-        "phpunit/PHPUnit": "~4.0"
+        "phpunit/PHPUnit": "~4.0",
+        "athletic/athletic": "dev-master"
     }
 }