Add psr/http-factory as explicit dependency

Author: JaZo

composer.json

@@ -26,6 +26,7 @@
         "danielstjules/stringy": "^3.1",
         "php-http/discovery": "^1.4",
         "php-http/mock-client": "^1.5",
+        "psr/http-factory": "^1.0",
         "psr/http-message": "^1.0"
     },
     "require-dev": {