Downgrade to phpunit 5.3.5 as 5.4.* requires php >= 5.6

Author: richardmiller-zz

composer.json

@@ -17,7 +17,7 @@
         "php": ">=5.5"
     },
     "require-dev": {
-        "phpunit/phpunit": "5.4.*",
+        "phpunit/phpunit": "5.3.5",
         "phpdocumentor/phpdocumentor": "2.*",
         "predis/predis": "1.0.*",
         "guzzlehttp/guzzle": "5.*",