[Checkins] [zopefoundation/zope.dublincore] 763a2f: Add missing extra.

[Michael Howitz]

  Branch: refs/heads/lint
  Home:   https://github.com/zopefoundation/zope.dublincore
  Commit: 763a2fa4221b420d586734ba87f2795cadfffa6b
      https://github.com/zopefoundation/zope.dublincore/commit/763a2fa4221b420d586734ba87f2795cadfffa6b
  Author: Michael Howitz <mh at gocept.com>
  Date:   2020-10-02 (Fri, 02 Oct 2020)

  Changed paths:
    M tox.ini

  Log Message:
  -----------
  Add missing extra.