Update fetch_mailinglist.R

[anisfeld]

I had an error where the following code created an error, but updating the dependencies seemed to fix the problem. I think in older versions of purrr::list_modify didn't work this way.

 elements <-
    purrr::map(
      elements,
      purrr::list_modify,
      responseHistory = purrr::zap(),
      emailHistory = purrr::zap()
    )