Merge pull request #60 from Nyholm/class-constant

We are using ::class which is php 5.5

Author: dbu

composer.json

@@ -11,7 +11,7 @@
         }
     ],
     "require": {
-        "php": "^5.4 || ^7.0"
+        "php": "^5.5|^7.0"
     },
     "require-dev": {
         "php-http/httplug": "^1.0",