async_hooks: fix reference in code comment

PR-URL: nodejs/node#15748
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Andreas Madsen <amwebdk@gmail.com>

lib/async_hooks.js

@@ -7,8 +7,8 @@ const errors = require('internal/errors');
  * hooks for each type.
  *
  * async_id_fields is a Float64Array wrapping the double array of
- * Environment::AsyncHooks::uid_fields_[]. Each index contains the ids for the
- * various asynchronous states of the application. These are:
+ * Environment::AsyncHooks::async_id_fields_[]. Each index contains the ids for
+ * the various asynchronous states of the application. These are:
  *  kExecutionAsyncId: The async_id assigned to the resource responsible for the
  *    current execution stack.
  *  kTriggerAsyncId: The trigger_async_id of the resource responsible for