Lowered requirement to support PHP 5.5

composer.json

@@ -26,7 +26,7 @@
     },
     "require-dev": {
         "phpunit/phpunit": "~4.8|~5.7",
-        "zendframework/zend-diactoros": "^1.7"
+        "zendframework/zend-diactoros": "^1.4"
     },
     "autoload": {
         "psr-4": {