Allow rollback to Rails 5.1
Allow rollback to Rails 5.1

See https://edgeguides.rubyonrails.org/upgrading_ruby_on_rails.html#expiry-in-signed-or-encrypted-cookie-is-now-embedded-in-the-cookies-values

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