Allow psr/http-message ^2.0

Requires php: ^7.2 || ^8.0
Closes reactphp#513

Author: valzargaming

composer.json

@@ -29,7 +29,7 @@
         "php": ">=7.1",
         "evenement/evenement": "^3.0 || ^2.0 || ^1.0",
         "fig/http-message-util": "^1.1",
-        "psr/http-message": "^1.0",
+        "psr/http-message": "^2.0 || ^1.0",
         "react/event-loop": "^1.2",
         "react/promise": "^3.2 || ^2.3 || ^1.2.1",
         "react/socket": "^1.16",