tests: update py3 test since json fields are now sorted
The fields have been sorted since 814151cd8c4a (logcmdutil: rewrite
jsonchangeset printer to be backed by jsonformatter, 2018-04-13), and
the test case has thus been failing since that commit.
Differential Revision: https://phab.mercurial-scm.org/D3570
#require docutils gettext
$ $TESTDIR/check-gendoc el
checking for parse errors