Be less restrict in phpunit versions (#7)

* Be less restrict in phpunit versions

* Minor

Author: Nyholm

composer.json

@@ -11,13 +11,13 @@
         }
     ],
     "require": {
-        "php": "^5.5|^7.0",
+        "php": "^5.5 || ^7.0",
         "psr/http-message": "^1.0",
-        "php-http/message-factory": "^1.0",
+        "php-http/message-factory": "^1.0.2",
         "php-http/discovery": "^1.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^5.4",
+        "phpunit/phpunit": "^4.8 || ^5.4",
         "php-http/message": "^1.0",
         "zendframework/zend-diactoros": "^1.3.5"
     },