[Checkins] [zopefoundation/ZODB] 25f66d: doc: fix typo _p_changed

[Jérome Perrin]

  Branch: refs/heads/master
  Home:   https://github.com/zopefoundation/ZODB
  Commit: 25f66d34f710679bef37a14f2acf775b5002a726
      https://github.com/zopefoundation/ZODB/commit/25f66d34f710679bef37a14f2acf775b5002a726
  Author: Jérome Perrin <jerome at nexedi.com>
  Date:   2020-09-04 (Fri, 04 Sep 2020)

  Changed paths:
    M doc/tutorial.rst

  Log Message:
  -----------
  doc: fix typo _p_changed

To manually mark an object modified, `_p_changed` attribute must be set, no `_p_changed__`