[Checkins] [zopefoundation/BTrees] 0bc1bd: Add the appveyor magic to install Python 3.8

[Marius Gedminas]

  Branch: refs/heads/py38
  Home:   https://github.com/zopefoundation/BTrees
  Commit: 0bc1bd5fef7f490afcf9a969cbfa46dbf97a7269
      https://github.com/zopefoundation/BTrees/commit/0bc1bd5fef7f490afcf9a969cbfa46dbf97a7269
  Author: Marius Gedminas <marius at gedmin.as>
  Date:   2019-11-06 (Wed, 06 Nov 2019)

  Changed paths:
    M appveyor.yml

  Log Message:
  -----------
  Add the appveyor magic to install Python 3.8