Added fallback for session secret
Added fallback for session secret

This fallback is added to ensure a session secret for the app
is always set/available in case the proper ENV variable is missing

https://github.com/sinatra/sinatra/issues/1187#issuecomment-255042768

aitbw/af_maracay,aitbw/af_maracay,aitbw/af_maracay