message: Alternate state for button when user & premium
diff: if user && !user.isPremium()
  button.Button.Button--size-lg.Button--fill( disabled )
  | Your current plan
  + else if user && user.isPremium()
  + button.Button.Button--size-lg.Button--fill( disabled )
  + | Join Basic
  else
  a.Button.Button--size-lg.Button--fill( href='/sign_up' )
  | Join Basic
  