Fix Observation#check_time intermittent bug
Fix Observation#check_time intermittent bug

Example:
https://travis-ci.org/github/MushroomObserver/mushroom-observer/builds/717764885

For solution, see https://docs.rubocop.org/rubocop-rails/2.7/cops_rails.html#railsdate

JoeCohen/mushroom-observer,MushroomObserver/mushroom-observer,JoeCohen/mushroom-observer,JoeCohen/mushroom-observer,MushroomObserver/mushroom-observer,JoeCohen/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,JoeCohen/mushroom-observer,JoeCohen/mushroom-observer,JoeCohen/mushroom-observer,MushroomObserver/mushroom-observer