build: allow plugin php-http/discovery

Author: JaZo

composer.json

@@ -57,5 +57,10 @@
         }
     },
     "minimum-stability": "dev",
-    "prefer-stable": true
+    "prefer-stable": true,
+    "config": {
+        "allow-plugins": {
+            "php-http/discovery": true
+        }
+    }
 }