n-api: fix memory leak in napi_async_destroy()

This is a cherry-pick patch from upstream[1].

[1] nodejs/node@87cb1f5

PR-URL: #213
Reviewed-By: Michael Dawson <[email protected]>

Author: romandev

src/node_api.cc

@@ -2855,6 +2855,8 @@ napi_status napi_async_destroy(napi_env env,
       reinterpret_cast<node::async_context*>(async_context);
   node::EmitAsyncDestroy(isolate, *node_async_context);
 
+  delete node_async_context;
+
   return napi_clear_last_error(env);
 }