michael_welcome:
  post_id: 1
  person_id: 1
  first_post_id: 2

michael_authorless:
  post_id: 3
  person_id: 1
  first_post_id: 3

michael_welcome:
  post_id: 1
  person: michael
  first_post_id: 2

michael_authorless:
  post_id: 3
  person: michael
  first_post_id: 3

Fix random test failure of test_create_resets_cached_counters
Fix random test failure of test_create_resets_cached_counters

- In earlier commit, I removed setting id manually for readers fixtures
  but that did not fix the randomly failing
  test_create_resets_cached_counters
  from has_many_associations tests.
- Because the problem was with the `person_id` of the readers. As it is
  set to 1 in fixtures, if a post gets created with id 1 then that post
  automatically has 2 readers.
- Fixed by removing the person_id.
