Update composer.json

Author: AndrewCarterUK

composer.json

@@ -18,7 +18,7 @@
         "symfony/console": "~2.5|~3.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "~5.0",
+        "phpunit/phpunit": "~4.0|~5.0",
         "satooshi/php-coveralls": "~1.0"
     },
     "autoload": {