Allow Laravel 5.6 (#435)

* Update composer.json

* Update composer.json

Author: SjorsO

composer.json

@@ -12,11 +12,11 @@
     ],
     "require": {
         "php": ">=5.4.0",
-        "illuminate/support": "5.5.*"
+        "illuminate/support": "5.5.*|5.6.*"
     },
     "require-dev": {
-        "orchestra/testbench": "3.5.*",
-        "phpunit/phpunit": "~6.0"
+        "orchestra/testbench": "3.5.*|3.6.*",
+        "phpunit/phpunit": "~6.0|~7.0"
     },
     "autoload": {
         "psr-4": {