laravel 6 support and phpunit 8 upgrade

Author: mtrajano

composer.json

@@ -9,8 +9,9 @@
         }
     ],
     "require-dev": {
-        "orchestra/testbench": "~3.0",
-        "phpunit/phpunit": "6.*"
+        "php": ">=7.0",
+        "orchestra/testbench": "~4.0",
+        "phpunit/phpunit": "8.3.*"
     },
     "autoload": {
         "files": [