TASK: Added phpunit/phpunit as required package for development

composer.json

@@ -29,7 +29,8 @@
     "symfony/filesystem": "^3.0"
   },
   "require-dev": {
-    "composer/composer": "^1.4"
+    "composer/composer": "^1.4",
+    "phpunit/phpunit": "^5.7"
   },
   "extra": {
     "class": "Higidi\\ComposerPhpCSStandardsPlugin\\Plugin"