Drop league/uri v6 support

Author: kelunik

composer.json

@@ -36,7 +36,7 @@
         "amphp/http-client": "^5",
         "amphp/socket": "^2.2",
         "amphp/websocket": "^2",
-        "league/uri": "^6.8|^7.1",
+        "league/uri": "^7.1",
         "psr/http-message": "^1|^2",
         "revolt/event-loop": "^1"
     },