Try to fix dependency versions for PHP 7.2 compatibility

Author: kylekatarnls

composer.json

@@ -28,8 +28,8 @@
     "minimum-stability": "stable",
     "require": {
         "php": ">=5.5.0",
-        "phpunit/phpunit": ">=4.8 <6.0",
-        "phpunit/php-code-coverage": ">=2.2 <4.0",
+        "phpunit/phpunit": "^4.8 || ^5.7",
+        "phpunit/php-code-coverage": "^2.2 || ^4.0 || ^5.2",
         "squizlabs/php_codesniffer": "^2.8",
         "symfony/console": "^3.2",
         "codeclimate/php-test-reporter": "^0.4.0"