[Checkins] [zopefoundation/Zope] 802130: Fix migration documentation

[Michael Howitz]

  Branch: refs/heads/icemac-patch-1
  Home:   https://github.com/zopefoundation/Zope
  Commit: 8021301fc5d205e5fc5e2636fc5167ed678526fd
      https://github.com/zopefoundation/Zope/commit/8021301fc5d205e5fc5e2636fc5167ed678526fd
  Author: Michael Howitz <mac at gmx.net>
  Date:   2019-06-24 (Mon, 24 Jun 2019)

  Changed paths:
    M docs/zope4/migration/zodb.rst

  Log Message:
  -----------
  Fix migration documentation

The main change is not to convert the ZODB in Python 2 as this is not the preferred way and the second attempt in Python 3 will fail because the ZODB is already converted.