[Checkins] [zopefoundation/zope.interface] f3622e: Attempt workaround for virtualenv 20.0 failures.

[Jason Madden]

  Branch: refs/heads/issue171
  Home:   https://github.com/zopefoundation/zope.interface
  Commit: f3622eb8d750801d0169509fe5d34d9675919844
      https://github.com/zopefoundation/zope.interface/commit/f3622eb8d750801d0169509fe5d34d9675919844
  Author: Jason Madden <jamadden at gmail.com>
  Date:   2020-02-10 (Mon, 10 Feb 2020)

  Changed paths:
    M .travis.yml

  Log Message:
  -----------
  Attempt workaround for virtualenv 20.0 failures.

See https://github.com/zopefoundation/zope.interface/pull/174#issuecomment-584154877