message: Update README.md
  typo in code
diff: @@ -64,7 +64,7 @@ In Xero a user can belong to multiple organisations. Tokens are ultimately assoc
  const newXeroClient = new XeroClient()
  const newTokenSet = await newXeroClient.refreshWithRefreshToken(xero_client_id, xero_client_secret, tokenSet.refresh_token)
  // refreshWithRefreshToken calls setAccessToken() so the refreshed token will be stored on newXeroClient
  - await newXeroClient.accountingApi.getInvoices('my-tenant-uuid))
  + await newXeroClient.accountingApi.getInvoices('my-tenant-uuid)
  ```
  ---
  