Update composer.json

Author: yatsenkolesh

composer.json

@@ -14,6 +14,6 @@
         "yatsenkolesh/php-curlasync": "^0.0.3"
     },
      "autoload": {
-        "psr-4": ["/"]
+        "psr-4":  {"Async\\": "src/"}
     }
 }