Composer version fix

composer.json

@@ -26,7 +26,7 @@
     },
     "require-dev": {
 		"rncryptor/spec": "3.0.1",
-		"phpunit/phpunit": "~5.7"
+		"phpunit/phpunit": ">=4.8 <6.0"
     },
     "autoload": {
         "psr-0": {