Require at least v7 of phpcsfixer

Author: nWidart

composer.json

@@ -32,7 +32,7 @@
     "phpunit/phpunit": "~6.0",
     "orchestra/testbench": "3.5.*",
     "fzaninotto/faker": "~1.5",
-    "friendsofphp/php-cs-fixer": "^2.4"
+    "friendsofphp/php-cs-fixer": "^2.7"
   },
   "autoload-dev": {
     "psr-4": {