Use PHPUnit ^6.5

Author: pamil

composer.json

@@ -5,7 +5,7 @@
     "license": "MIT",
     "require": {
         "php": "^7.1",
-        
+
         "sylius/sylius": "^1.0.4"
     },
     "require-dev": {
@@ -22,7 +22,7 @@
         "lakion/mink-debug-extension": "^1.2.3",
         "phpspec/phpspec": "^3.2",
         "phpstan/phpstan-shim": "^0.9.2",
-        "phpunit/phpunit": "^5.6",
+        "phpunit/phpunit": "^6.5",
         "se/selenium-server-standalone": "^2.52",
         "sylius-labs/coding-standard": "^1.0",
         "symplify/easy-coding-standard": "^2.4"