chore(dependencies): adjust dependencies for laravel 6

Author: ArturMoczulski

composer.json

@@ -21,11 +21,11 @@
         "rollbar/rollbar": "^2"
     },
     "require-dev": {
-        "orchestra/testbench": "~3.6",
+        "orchestra/testbench": "^4",
         "mockery/mockery": "^1",
         "satooshi/php-coveralls": "^1.0",
         "squizlabs/php_codesniffer": "3.*",
-        "phpunit/phpunit": "~7.0"
+        "phpunit/phpunit": "^8"
     },
     "autoload": {
         "psr-4": {