Replaced php-http/message-factory with psr/http-factory

Author: erickr

composer.json

@@ -17,12 +17,12 @@
         "php-http/client-implementation": "^1.0",
         "php-http/httplug": "^1.0 || ^2.0",
         "php-http/message": "^1.0",
-        "php-http/message-factory": "^1.0",
         "php-xapi/exception": "^1.0",
         "php-xapi/model": "^4.0",
         "php-xapi/serializer": "^4.0",
         "php-xapi/symfony-serializer": "^3.0",
-        "psr/http-message": "^1.0"
+        "psr/http-message": "^1.0",
+        "psr/http-factory": "^1.0"
     },
     "require-dev": {
         "phpspec/phpspec": "^6.0 || ^7.0",