Require PHPUnit 7 as we minimum require PHP 7.1

Author: carusogabriel

composer.json

@@ -12,7 +12,7 @@
 	"require": {
 		"php": "~7.1",
 		"phpstan/phpstan": "^0.10",
-		"phpunit/phpunit": "^6.3 || ~7.0"
+		"phpunit/phpunit": "^7.0"
 	},
 	"require-dev": {
 		"consistence/coding-standard": "^2.0",