Require amphp/parallel 2.1

Author: kelunik

composer.json

@@ -36,7 +36,7 @@
         "amphp/amp": "^3",
         "amphp/byte-stream": "^2",
         "amphp/cache": "^2",
-        "amphp/parallel": "^2",
+        "amphp/parallel": "^2.1",
         "amphp/sync": "^2",
         "revolt/event-loop": "^1 || ^0.2.1"
     },