Use updated testbench-dusk version

Author: mpociot

composer.json

@@ -23,8 +23,8 @@
         "spatie/browsershot": "^3.22"
     },
     "require-dev": {
-        "orchestra/testbench-dusk": "^3.5",
-        "phpunit/phpunit": "^6.0"
+        "orchestra/testbench-dusk": "3.6.x@dev",
+        "phpunit/phpunit": "^7.0"
     },
     "autoload": {
         "psr-4": {