fix: resolved undefined stack in error issue

Author: Vikram Kalta

lib/core/concurrency-queue.js

@@ -155,7 +155,8 @@ export function ConcurrencyQueue ({ axios, config }) {
           code: 'Unauthorized',
           message: 'Unable to refresh token',
           name: 'Token Error',
-          config: queueItem.request
+          config: queueItem.request,
+          stack: (error instanceof Error) ? error.stack : null,
         })
       })
       this.queue = []