[HttpClient] fix missing dep

Author: nicolas-grekas

composer.json

@@ -33,6 +33,7 @@
         "nyholm/psr7": "^1.0",
         "php-http/httplug": "^1.0|^2.0",
         "psr/http-client": "^1.0",
+        "php-http/message-factory": "^1.0",
         "symfony/dependency-injection": "^4.3|^5.0",
         "symfony/http-kernel": "^4.4.13",
         "symfony/process": "^4.2|^5.0"