Fix random CI failure due to non-deterministic sorting order
Fix random CI failure due to non-deterministic sorting order

An `author` has a lots of `posts` in the fixtures, so the result of
`author.post` and finding a `post` by `author_id` is non-deterministic.

https://travis-ci.org/rails/rails/jobs/504332292#L1202-L1208

kddeisz/rails,kmcphillips/rails,Stellenticket/rails,bogdanvlviv/rails,yhirano55/rails,repinel/rails,lcreid/rails,notapatch/rails,BlakeWilliams/rails,rafaelfranca/omg-rails,mechanicles/rails,vipulnsward/rails,notapatch/rails,Vasfed/rails,Erol/rails,yalab/rails,joonyou/rails,schuetzm/rails,yahonda/rails,Erol/rails,georgeclaghorn/rails,kddeisz/rails,rails/rails,EmmaB/rails-1,kddeisz/rails,jeremy/rails,eileencodes/rails,rails/rails,flanger001/rails,esparta/rails,repinel/rails,tgxworld/rails,vipulnsward/rails,yhirano55/rails,yawboakye/rails,BlakeWilliams/rails,gauravtiwari/rails,Edouard-chin/rails,betesh/rails,shioyama/rails,Erol/rails,Vasfed/rails,fabianoleittes/rails,starknx/rails,arunagw/rails,mechanicles/rails,tgxworld/rails,joonyou/rails,georgeclaghorn/rails,Edouard-chin/rails,Erol/rails,kmcphillips/rails,BlakeWilliams/rails,gauravtiwari/rails,jeremy/rails,prathamesh-sonpatki/rails,joonyou/rails,tgxworld/rails,yawboakye/rails,joonyou/rails,lcreid/rails,BlakeWilliams/rails,palkan/rails,esparta/rails,Envek/rails,MSP-Greg/rails,georgeclaghorn/rails,schuetzm/rails,esparta/rails,vipulnsward/rails,esparta/rails,flanger001/rails,kmcphillips/rails,betesh/rails,rails/rails,prathamesh-sonpatki/rails,arunagw/rails,jeremy/rails,yawboakye/rails,yalab/rails,eileencodes/rails,Stellenticket/rails,Vasfed/rails,Envek/rails,yhirano55/rails,tjschuck/rails,EmmaB/rails-1,yalab/rails,Envek/rails,tjschuck/rails,shioyama/rails,arunagw/rails,iainbeeston/rails,flanger001/rails,Edouard-chin/rails,betesh/rails,rafaelfranca/omg-rails,repinel/rails,bogdanvlviv/rails,MSP-Greg/rails,flanger001/rails,iainbeeston/rails,yahonda/rails,yawboakye/rails,gauravtiwari/rails,betesh/rails,repinel/rails,rails/rails,bogdanvlviv/rails,prathamesh-sonpatki/rails,Stellenticket/rails,palkan/rails,jeremy/rails,prathamesh-sonpatki/rails,kmcphillips/rails,iainbeeston/rails,Vasfed/rails,palkan/rails,notapatch/rails,Edouard-chin/rails,mechanicles/rails,arunagw/rails,yalab/rails,notapatch/rails,tjschuck/rails,rafaelfranca/omg-rails,yahonda/rails,tjschuck/rails,eileencodes/rails,EmmaB/rails-1,kddeisz/rails,schuetzm/rails,schuetzm/rails,iainbeeston/rails,yhirano55/rails,fabianoleittes/rails,vipulnsward/rails,lcreid/rails,eileencodes/rails,lcreid/rails,Envek/rails,tgxworld/rails,starknx/rails,bogdanvlviv/rails,yahonda/rails,MSP-Greg/rails,starknx/rails,mechanicles/rails,shioyama/rails,Stellenticket/rails,palkan/rails,fabianoleittes/rails,MSP-Greg/rails,fabianoleittes/rails,georgeclaghorn/rails,shioyama/rails