Downgrade phpunit to 4.8.26 to allow for PHP 5.3

Author: richardmiller-zz

composer.json

@@ -17,7 +17,7 @@
         "php": ">=5.5"
     },
     "require-dev": {
-        "phpunit/phpunit": "5.3.5",
+        "phpunit/phpunit": "4.8.26",
         "phpdocumentor/phpdocumentor": "2.*",
         "predis/predis": "1.0.*",
         "guzzlehttp/guzzle": "5.*",