add whoops to dev dependencies

composer.json

@@ -11,6 +11,7 @@
         "laravel/tinker": "~1.0"
     },
     "require-dev": {
+        "filp/whoops": "~2.0",
         "fzaninotto/faker": "~1.4",
         "mockery/mockery": "0.9.*",
         "phpunit/phpunit": "~6.0"