Changes Session.find to Session.find_by in DemoMode::Demoable#current_demo_session to prevent a Not Found exception when the session is no longer in the database, e.g., after resetting the database.
Checks that the current_demo_session is not nil in DemoMode::Demoable#demo_splash!.
This addresses issue https://github.com/Betterment/demo_mode/issues/7.
Session.findtoSession.find_byinDemoMode::Demoable#current_demo_sessionto prevent a Not Found exception when the session is no longer in the database, e.g., after resetting the database.current_demo_sessionis notnilinDemoMode::Demoable#demo_splash!.