Add PHPUnit >=7.0.0,<7.1.0 to the dependencies

Author: lbajsarowicz

composer.json

@@ -30,7 +30,7 @@
         "goaop/framework": "2.2.0",
         "codacy/coverage": "^1.4",
         "phpmd/phpmd": "^2.6.0",
-        "phpunit/phpunit": "~6.5.0",
+        "phpunit/phpunit": "~6.5.0 || ~7.0.0",
         "rregeer/phpunit-coverage-check": "^0.1.4",
         "php-coveralls/php-coveralls": "^1.0",
         "symfony/stopwatch": "~3.4.6"