Require version 2.1 of simple-bus/asynchronous

Author: Nyholm

composer.json

@@ -16,7 +16,7 @@
         "php": ">=5.4",
         "beberlei/assert": "~2.0",
         "simple-bus/message-bus": "~2.0",
-        "simple-bus/asynchronous": "~2.0",
+        "simple-bus/asynchronous": "~2.1",
         "simple-bus/symfony-bridge": "~4.0",
         "symfony/framework-bundle": "~2.0|~3.0"
     },